<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 16px 12px;
      user-select: none;
    }

    .equation-bar {
      font-size: 26px;
      font-weight: 800;
      letter-spacing: 0.5px;
      margin-bottom: 6px;
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .c-blue { color: #2563eb; }
    .c-orange { color: #ea580c; }
    .c-purple { color: #7c3aed; }
    .eq-part {
      padding: 2px 6px;
      border-radius: 6px;
      transition: background 0.3s ease, transform 0.3s ease;
    }
    .eq-part.active-blue { background: #dbeafe; }
    .eq-part.active-orange { background: #ffedd5; }
    .eq-part.active-purple { background: #ede9fe; }

    .diagram-area {
      width: 100%;
      max-width: 580px;
      position: relative;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    .axis-line { stroke: #94a3b8; stroke-width: 3; stroke-linecap: round; }
    .tick-line { stroke: #94a3b8; stroke-width: 2.5; stroke-linecap: round; }
    .tick-label { font-size: 15px; font-weight: 600; fill: #64748b; text-anchor: middle; }
    .tick-zero { font-size: 16px; font-weight: 800; fill: #1e2945; }

    /* Animated arrows and elements */
    .arrow-path {
      fill: none;
      stroke-linecap: round;
      transition: opacity 0.4s ease, stroke-dashoffset 0.8s ease-out;
    }
    .arrow-step1 {
      stroke: #2563eb;
      stroke-width: 4;
      stroke-dasharray: 400;
      stroke-dashoffset: 400;
      opacity: 0;
    }
    .arrow-step2 {
      stroke: #ea580c;
      stroke-width: 4;
      stroke-dasharray: 600;
      stroke-dashoffset: 600;
      opacity: 0;
    }
    .label-step1, .label-step2, .result-group {
      opacity: 0;
      transition: opacity 0.4s ease, transform 0.4s ease;
    }

    .visible-1 .arrow-step1 { opacity: 1; stroke-dashoffset: 0; }
    .visible-1 .label-step1 { opacity: 1; }

    .visible-2 .arrow-step2 { opacity: 1; stroke-dashoffset: 0; }
    .visible-2 .label-step2 { opacity: 1; }

    .visible-3 .result-group { opacity: 1; transform: scale(1); }

    /* Controls */
    .controls {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: center;
      gap: 8px;
      margin-top: 8px;
    }
    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 8px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
      transition: all 0.2s ease;
    }
    .btn:hover { background: #e2e8f0; }
    .btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }
    .btn-play {
      background: #2563eb;
      color: #ffffff;
      border-color: #2563eb;
      font-weight: 700;
    }
    .btn-play:hover { background: #1d4ed8; }
  </style>
</head>
<body>

  <div class="equation-bar">
    <span id="eqPart1" class="eq-part c-blue">3</span>
    <span>+</span>
    <span id="eqPart2" class="eq-part c-orange">(-5)</span>
    <span>=</span>
    <span id="eqPart3" class="eq-part c-purple">-2</span>
  </div>

  <div class="diagram-area" id="diagramContainer">
    <svg viewBox="0 0 550 220" id="numberLineSvg">
      <defs>
        
        <marker id="arrow-blue" markerWidth="8" markerHeight="8" refX="6" refY="4" orient="auto">
          <polygon points="0 1, 8 4, 0 7" fill="#2563eb" />
        </marker>
        
        <marker id="arrow-orange" markerWidth="8" markerHeight="8" refX="6" refY="4" orient="auto">
          <polygon points="0 1, 8 4, 0 7" fill="#ea580c" />
        </marker>
      </defs>

      
      <g id="step1Group">
        
        <path class="arrow-path arrow-step1" d="M 275 165 C 275 110, 410 110, 410 162" marker-end="url(#arrow-blue)" />
        <g class="label-step1">
          <rect x="322" y="94" width="40" height="24" rx="6" fill="#dbeafe" />
          <text x="342" y="111" fill="#2563eb" font-size="14" font-weight="800" text-anchor="middle">+3</text>
        </g>
      </g>

      
      <g id="step2Group">
        
        <path class="arrow-path arrow-step2" d="M 410 165 C 410 40, 185 40, 185 162" marker-end="url(#arrow-orange)" />
        <g class="label-step2">
          <rect x="278" y="32" width="40" height="24" rx="6" fill="#ffedd5" />
          <text x="298" y="49" fill="#ea580c" font-size="14" font-weight="800" text-anchor="middle">-5</text>
        </g>
      </g>

      
      <line x1="25" y1="170" x2="525" y2="170" class="axis-line" />
      <polygon points="25 166, 15 170, 25 174" fill="#94a3b8" />
      <polygon points="525 166, 535 170, 525 174" fill="#94a3b8" />

      
      
      <line x1="50" y1="162" x2="50" y2="178" class="tick-line" />
      <text x="50" y="196" class="tick-label">-5</text>

      
      <line x1="95" y1="162" x2="95" y2="178" class="tick-line" />
      <text x="95" y="196" class="tick-label">-4</text>

      
      <line x1="140" y1="162" x2="140" y2="178" class="tick-line" />
      <text x="140" y="196" class="tick-label">-3</text>

      
      <line x1="185" y1="162" x2="185" y2="178" class="tick-line" />
      <text x="185" y="196" class="tick-label">-2</text>

      
      <line x1="230" y1="162" x2="230" y2="178" class="tick-line" />
      <text x="230" y="196" class="tick-label">-1</text>

      
      <line x1="275" y1="158" x2="275" y2="182" stroke="#1e2945" stroke-width="3" stroke-linecap="round" />
      <text x="275" y="197" class="tick-label tick-zero">0</text>
      <circle cx="275" cy="170" r="4" fill="#1e2945" />

      
      <line x1="320" y1="162" x2="320" y2="178" class="tick-line" />
      <text x="320" y="196" class="tick-label">+1</text>

      
      <line x1="365" y1="162" x2="365" y2="178" class="tick-line" />
      <text x="365" y="196" class="tick-label">+2</text>

      
      <line x1="410" y1="162" x2="410" y2="178" class="tick-line" />
      <text x="410" y="196" class="tick-label">+3</text>

      
      <line x1="455" y1="162" x2="455" y2="178" class="tick-line" />
      <text x="455" y="196" class="tick-label">+4</text>

      
      <line x1="500" y1="162" x2="500" y2="178" class="tick-line" />
      <text x="500" y="196" class="tick-label">+5</text>

      
      <g id="step3Group" class="result-group">
        
        <circle cx="185" cy="170" r="14" fill="#ede9fe" />
        
        <circle cx="185" cy="170" r="7" fill="#7c3aed" />
        
        <rect x="135" y="130" width="100" height="24" rx="6" fill="#7c3aed" />
        <text x="185" y="146" fill="#ffffff" font-size="12" font-weight="700" text-anchor="middle">Result: -2</text>
        <polygon points="181 154, 189 154, 185 158" fill="#7c3aed" />
      </g>
    </svg>
  </div>

  
  <div class="controls">
    <button class="btn btn-play" id="playBtn" aria-label="Play or Pause">⏸ Pause</button>
    <button class="btn active" id="btnStep1">1: Start +3</button>
    <button class="btn" id="btnStep2">2: Move -5</button>
    <button class="btn" id="btnStep3">3: Result -2</button>
  </div>

  <script>
    const container = document.getElementById('diagramContainer');
    const stepBtns = [
      document.getElementById('btnStep1'),
      document.getElementById('btnStep2'),
      document.getElementById('btnStep3')
    ];
    const eqParts = [
      document.getElementById('eqPart1'),
      document.getElementById('eqPart2'),
      document.getElementById('eqPart3')
    ];
    const playBtn = document.getElementById('playBtn');

    let currentStep = 1;
    let isPlaying = true;
    let timer = null;
    const STEP_DURATION = 3200;

    function renderStep(step) {
      currentStep = step;

      // Update diagram SVG classes
      container.classList.remove('visible-1', 'visible-2', 'visible-3');
      if (step >= 1) container.classList.add('visible-1');
      if (step >= 2) container.classList.add('visible-2');
      if (step >= 3) container.classList.add('visible-3');

      // Update button active state
      stepBtns.forEach((btn, idx) => {
        btn.classList.toggle('active', idx + 1 === step);
      });

      // Update equation active highlights
      eqParts[0].classList.toggle('active-blue', step === 1);
      eqParts[1].classList.toggle('active-orange', step === 2);
      eqParts[2].classList.toggle('active-purple', step === 3);
    }

    function nextStep() {
      let next = currentStep + 1;
      if (next > 3) next = 1;
      renderStep(next);
    }

    function startAutoPlay() {
      if (timer) clearInterval(timer);
      isPlaying = true;
      playBtn.textContent = '⏸ Pause';
      timer = setInterval(nextStep, STEP_DURATION);
    }

    function pauseAutoPlay() {
      if (timer) clearInterval(timer);
      isPlaying = false;
      playBtn.textContent = '▶ Play';
    }

    playBtn.addEventListener('click', () => {
      if (isPlaying) {
        pauseAutoPlay();
      } else {
        startAutoPlay();
      }
    });

    stepBtns.forEach((btn, idx) => {
      btn.addEventListener('click', () => {
        pauseAutoPlay();
        renderStep(idx + 1);
      });
    });

    // Initialize
    renderStep(1);
    startAutoPlay();
  </script>
</body>
</html>

Modeling Integer Addition with Number Lines

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      padding: 12px;
      user-select: none;
    }
    .diagram-wrap {
      width: 100%;
      max-width: 620px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
    }
    .stepper-nav {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
      width: 100%;
    }
    .step-btn {
      appearance: none;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #475569;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 20px;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .step-btn:hover {
      background: #f1f5f9;
    }
    .step-btn.active {
      background: #ea580c;
      border-color: #ea580c;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(234, 88, 12, 0.3);
    }
    .play-btn {
      appearance: none;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #1e2945;
      width: 32px;
      height: 32px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      font-size: 13px;
      transition: all 0.2s ease;
    }
    .play-btn:hover {
      background: #f1f5f9;
    }
    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }
    .axis-line {
      stroke: #64748b;
      stroke-width: 2.5;
      stroke-linecap: round;
    }
    .tick-line {
      stroke: #64748b;
      stroke-width: 2;
    }
    .tick-text {
      font-size: 14px;
      font-weight: 600;
      fill: #475569;
      text-anchor: middle;
      dominant-baseline: central;
    }
    .tick-text.highlight-zero {
      fill: #0f172a;
      font-weight: 700;
    }
    .tick-text.highlight-target {
      fill: #ea580c;
      font-weight: 800;
    }
    .arrow-path {
      fill: none;
      stroke: #ea580c;
      stroke-width: 3.5;
      stroke-linecap: round;
      transition: opacity 0.35s ease, stroke-dashoffset 0.5s ease;
    }
    .arrow-label {
      font-size: 15px;
      font-weight: 700;
      fill: #ea580c;
      text-anchor: middle;
      dominant-baseline: central;
      transition: opacity 0.35s ease;
    }
    .label-badge {
      fill: #fff7ed;
      stroke: #fdba74;
      stroke-width: 1.5;
      rx: 6;
      ry: 6;
    }
    .target-dot {
      fill: #ea580c;
      stroke: #ffffff;
      stroke-width: 2.5;
      transition: opacity 0.35s ease, transform 0.35s ease;
      transform-origin: 150px 180px;
    }
    .start-dot {
      fill: #64748b;
      stroke: #ffffff;
      stroke-width: 2;
    }
    .step-fade {
      opacity: 0;
      pointer-events: none;
    }
    .step-fade.visible {
      opacity: 1;
      pointer-events: auto;
    }
    .callout-group {
      transition: opacity 0.35s ease, transform 0.35s ease;
      transform-origin: 150px 246px;
    }
  </style>
</head>
<body>

<div class="diagram-wrap">
  <div class="stepper-nav">
    <button id="playBtn" class="play-btn" aria-label="Play/Pause">⏸</button>
    <button class="step-btn active" data-step="1">1. Start at 0 &amp; Move -2</button>
    <button class="step-btn" data-step="2">2. Move -4</button>
    <button class="step-btn" data-step="3">3. Sum is -6</button>
  </div>

  <svg viewBox="0 0 600 290" aria-label="Number line showing -2 plus -4 equals -6">
    <defs>
      
      <marker id="axisArrowLeft" markerWidth="8" markerHeight="8" refX="2" refY="4" orient="auto">
        <polygon points="7,1 1,4 7,7" fill="#64748b" />
      </marker>
      <marker id="axisArrowRight" markerWidth="8" markerHeight="8" refX="6" refY="4" orient="auto">
        <polygon points="1,1 7,4 1,7" fill="#64748b" />
      </marker>
      <marker id="jumpArrowHead" markerWidth="7" markerHeight="7" refX="5" refY="3.5" orient="auto">
        <polygon points="1,1 6,3.5 1,6" fill="#ea580c" />
      </marker>
      <filter id="shadow" x="-10%" y="-10%" width="130%" height="130%">
        <feDropShadow dx="0" dy="2" stdDeviation="2.5" flood-color="#000" flood-opacity="0.08" />
      </filter>
    </defs>

    
    <line x1="30" y1="180" x2="570" y2="180" class="axis-line" marker-start="url(#axisArrowLeft)" marker-end="url(#axisArrowRight)" />

    
    
    <g id="ticks">
      <line x1="50" y1="172" x2="50" y2="188" class="tick-line" />
      <text x="50" y="206" class="tick-text">-8</text>

      <line x1="100" y1="172" x2="100" y2="188" class="tick-line" />
      <text x="100" y="206" class="tick-text">-7</text>

      <line x1="150" y1="170" x2="150" y2="190" class="tick-line" style="stroke-width: 2.5; stroke: #ea580c;" />
      <text x="150" y="206" class="tick-text highlight-target">-6</text>

      <line x1="200" y1="172" x2="200" y2="188" class="tick-line" />
      <text x="200" y="206" class="tick-text">-5</text>

      <line x1="250" y1="172" x2="250" y2="188" class="tick-line" />
      <text x="250" y="206" class="tick-text">-4</text>

      <line x1="300" y1="172" x2="300" y2="188" class="tick-line" />
      <text x="300" y="206" class="tick-text">-3</text>

      <line x1="350" y1="172" x2="350" y2="188" class="tick-line" />
      <text x="350" y="206" class="tick-text">-2</text>

      <line x1="400" y1="172" x2="400" y2="188" class="tick-line" />
      <text x="400" y="206" class="tick-text">-1</text>

      <line x1="450" y1="168" x2="450" y2="192" class="tick-line" style="stroke-width: 2.5; stroke: #0f172a;" />
      <text x="450" y="206" class="tick-text highlight-zero">0</text>

      <line x1="500" y1="172" x2="500" y2="188" class="tick-line" />
      <text x="500" y="206" class="tick-text">+1</text>

      <line x1="550" y1="172" x2="550" y2="188" class="tick-line" />
      <text x="550" y="206" class="tick-text">+2</text>
    </g>

    
    <circle cx="450" cy="180" r="4.5" class="start-dot" />

    
    <g id="step1Group" class="step-fade visible">
      <path d="M 448 174 C 430 128, 370 128, 353 172" class="arrow-path" marker-end="url(#jumpArrowHead)" />
      <rect x="382" y="105" width="36" height="24" class="label-badge" />
      <text x="400" y="117" class="arrow-label">-2</text>
    </g>

    
    <g id="step1Dot" class="step-fade visible">
      <circle cx="350" cy="180" r="4" fill="#ea580c" />
    </g>

    
    <g id="step2Group" class="step-fade">
      <path d="M 348 174 C 310 82, 190 82, 153 172" class="arrow-path" marker-end="url(#jumpArrowHead)" />
      <rect x="232" y="70" width="36" height="24" class="label-badge" />
      <text x="250" y="82" class="arrow-label">-4</text>
    </g>

    
    <g id="step3Group" class="step-fade">
      
      <circle cx="150" cy="180" r="7" class="target-dot" />

      
      <g class="callout-group" filter="url(#shadow)">
        <polygon points="150,224 144,233 156,233" fill="#0f172a" />
        <rect x="75" y="233" width="150" height="34" rx="8" ry="8" fill="#0f172a" />
        <text x="150" y="250" fill="#ffffff" font-size="14" font-weight="700" text-anchor="middle" dominant-baseline="central">
          -2 + (-4) = -6
        </text>
      </g>
    </g>
  </svg>
</div>

<script>
  const stepBtns = document.querySelectorAll('.step-btn');
  const playBtn = document.getElementById('playBtn');
  const step1Group = document.getElementById('step1Group');
  const step1Dot = document.getElementById('step1Dot');
  const step2Group = document.getElementById('step2Group');
  const step3Group = document.getElementById('step3Group');

  let currentStep = 1;
  let isPlaying = true;
  let timer = null;

  function renderStep(step) {
    currentStep = step;
    stepBtns.forEach((btn, idx) => {
      btn.classList.toggle('active', idx + 1 === step);
    });

    if (step === 1) {
      step1Group.classList.add('visible');
      step1Dot.classList.add('visible');
      step2Group.classList.remove('visible');
      step3Group.classList.remove('visible');
    } else if (step === 2) {
      step1Group.classList.add('visible');
      step1Dot.classList.add('visible');
      step2Group.classList.add('visible');
      step3Group.classList.remove('visible');
    } else if (step === 3) {
      step1Group.classList.add('visible');
      step1Dot.classList.add('visible');
      step2Group.classList.add('visible');
      step3Group.classList.add('visible');
    }
  }

  function nextStep() {
    let next = currentStep + 1;
    if (next > 3) next = 1;
    renderStep(next);
  }

  function startAutoPlay() {
    isPlaying = true;
    playBtn.textContent = '⏸';
    clearInterval(timer);
    timer = setInterval(nextStep, 3200);
  }

  function stopAutoPlay() {
    isPlaying = false;
    playBtn.textContent = '▶';
    clearInterval(timer);
  }

  stepBtns.forEach(btn => {
    btn.addEventListener('click', () => {
      stopAutoPlay();
      renderStep(parseInt(btn.getAttribute('data-step'), 10));
    });
  });

  playBtn.addEventListener('click', () => {
    if (isPlaying) {
      stopAutoPlay();
    } else {
      nextStep();
      startAutoPlay();
    }
  });

  // Start initial auto-play
  startAutoPlay();
</script>

</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      color: #1e2945;
      background: #ffffff;
      padding: 16px 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }

    /* Directional Guide Banners */
    .guides-row {
      display: flex;
      gap: 10px;
      width: 100%;
      max-width: 580px;
      margin-bottom: 8px;
    }

    .guide-card {
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      padding: 10px 14px;
      border-radius: 12px;
      font-weight: 700;
      font-size: 14px;
      transition: opacity 0.2s ease, transform 0.2s ease;
    }

    .guide-neg {
      background: #fff3eb;
      color: #d9531e;
      border: 1.5px solid #fed7aa;
    }

    .guide-pos {
      background: #eff6ff;
      color: #1d4ed8;
      border: 1.5px solid #bfdbfe;
    }

    .arrow-icon {
      font-size: 18px;
      line-height: 1;
    }

    /* SVG Canvas Area */
    .visual-area {
      width: 100%;
      max-width: 600px;
      position: relative;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    /* Stepper & Controls */
    .controls {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: center;
      gap: 8px;
      margin-top: 12px;
      width: 100%;
      max-width: 580px;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      color: #1e2945;
      padding: 8px 14px;
      border-radius: 10px;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background-color 0.2s, box-shadow 0.2s;
    }

    .step-btn:focus {
      outline: none;
    }

    .step-btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
      box-shadow: 0 2px 8px rgba(30, 41, 69, 0.25);
    }

    .play-btn {
      background: #2563eb;
      color: #ffffff;
      border: 1.5px solid #2563eb;
      padding: 8px 16px;
      border-radius: 10px;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
    }

    .equation-badge {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 15px;
      font-weight: 700;
      color: #1e2945;
      letter-spacing: 0.5px;
    }
  </style>
</head>
<body>

  
  <div class="guides-row">
    <div class="guide-card guide-neg" id="cardNeg">
      <span class="arrow-icon">←</span>
      <span>− Negative: Move Left</span>
    </div>
    <div class="guide-card guide-pos" id="cardPos">
      <span>+ Positive: Move Right</span>
      <span class="arrow-icon">→</span>
    </div>
  </div>

  
  <div class="visual-area">
    <svg viewBox="0 0 600 230" preserveAspectRatio="xMidYMid meet">
      <defs>
        
        <marker id="arrow-axis" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 8 5 L 0 9 z" fill="#64748b"/>
        </marker>
        <marker id="arrow-blue" viewBox="0 0 10 10" refX="7" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#2563eb"/>
        </marker>
        <marker id="arrow-orange" viewBox="0 0 10 10" refX="7" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#ea580c"/>
        </marker>
      </defs>

      
      <line x1="25" y1="170" x2="575" y2="170" stroke="#64748b" stroke-width="3" stroke-linecap="round" marker-start="url(#arrow-axis)" marker-end="url(#arrow-axis)"/>

      
      
      
      <g id="ticks">
        
        <line x1="60" y1="160" x2="60" y2="180" stroke="#64748b" stroke-width="2"/>
        <text x="60" y="202" text-anchor="middle" font-size="14" font-weight="600" fill="#64748b">-6</text>

        
        <line x1="100" y1="162" x2="100" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="100" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">-5</text>

        
        <line x1="140" y1="162" x2="140" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="140" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">-4</text>

        
        <line x1="180" y1="162" x2="180" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="180" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">-3</text>

        
        <line x1="220" y1="158" x2="220" y2="182" stroke="#ea580c" stroke-width="2.5"/>
        <text x="220" y="203" text-anchor="middle" font-size="15" font-weight="700" fill="#ea580c">-2</text>

        
        <line x1="260" y1="162" x2="260" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="260" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">-1</text>

        
        <line x1="300" y1="154" x2="300" y2="186" stroke="#1e2945" stroke-width="3.5"/>
        <text x="300" y="205" text-anchor="middle" font-size="16" font-weight="800" fill="#1e2945">0</text>

        
        <line x1="340" y1="162" x2="340" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="340" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">+1</text>

        
        <line x1="380" y1="162" x2="380" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="380" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">+2</text>

        
        <line x1="420" y1="162" x2="420" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="420" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">+3</text>

        
        <line x1="460" y1="158" x2="460" y2="182" stroke="#2563eb" stroke-width="2.5"/>
        <text x="460" y="203" text-anchor="middle" font-size="15" font-weight="700" fill="#2563eb">+4</text>

        
        <line x1="500" y1="162" x2="500" y2="178" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="500" y="202" text-anchor="middle" font-size="14" font-weight="500" fill="#64748b">+5</text>

        
        <line x1="540" y1="160" x2="540" y2="180" stroke="#64748b" stroke-width="2"/>
        <text x="540" y="202" text-anchor="middle" font-size="14" font-weight="600" fill="#64748b">+6</text>
      </g>

      
      
      <g id="step1Group" style="opacity: 0; transition: opacity 0.4s ease;">
        <path d="M 300 162 Q 380 95, 456 162" fill="none" stroke="#2563eb" stroke-width="3" stroke-dasharray="none" marker-end="url(#arrow-blue)"/>
        <rect x="360" y="90" width="42" height="24" rx="6" fill="#eff6ff" stroke="#bfdbfe" stroke-width="1.5"/>
        <text x="381" y="107" text-anchor="middle" font-size="13" font-weight="700" fill="#1d4ed8">+4</text>
      </g>

      
      
      <g id="step2Group" style="opacity: 0; transition: opacity 0.4s ease;">
        <path d="M 460 162 Q 340 25, 224 162" fill="none" stroke="#ea580c" stroke-width="3" stroke-dasharray="none" marker-end="url(#arrow-orange)"/>
        <rect x="320" y="38" width="42" height="24" rx="6" fill="#fff3eb" stroke="#fed7aa" stroke-width="1.5"/>
        <text x="341" y="55" text-anchor="middle" font-size="13" font-weight="700" fill="#ea580c">−6</text>
      </g>

      
      <g id="tracker" style="transition: transform 0.45s cubic-bezier(0.34, 1.56, 0.64, 1);" transform="translate(300, 170)">
        <circle r="7" fill="#1e2945" stroke="#ffffff" stroke-width="2.5" />
        <circle r="12" fill="none" stroke="#1e2945" stroke-width="1.5" opacity="0.3"/>
      </g>
    </svg>
  </div>

  
  <div class="controls">
    <button class="step-btn active" id="btn0" onclick="setStep(0)">Start (0)</button>
    <button class="step-btn" id="btn1" onclick="setStep(1)">+4 Right</button>
    <button class="step-btn" id="btn2" onclick="setStep(2)">−6 Left</button>
    <div class="equation-badge" id="eqBadge">0</div>
    <button class="play-btn" id="playBtn" onclick="togglePlay()">▶ Play</button>
  </div>

  <script>
    const positions = [300, 460, 220]; // x coordinates for 0, +4, -2
    const equations = ["0", "0 + 4 = +4", "0 + 4 + (−6) = −2"];
    let currentStep = 0;
    let timer = null;

    function setStep(step) {
      currentStep = step;

      // Update marker position
      const tracker = document.getElementById('tracker');
      tracker.setAttribute('transform', `translate(${positions[step]}, 170)`);

      // Update arcs
      const s1 = document.getElementById('step1Group');
      const s2 = document.getElementById('step2Group');
      s1.style.opacity = step >= 1 ? '1' : '0';
      s2.style.opacity = step >= 2 ? '1' : '0';

      // Update buttons
      document.querySelectorAll('.step-btn').forEach((btn, idx) => {
        btn.classList.toggle('active', idx === step);
      });

      // Update equation text
      document.getElementById('eqBadge').textContent = equations[step];

      // Highlight active directional banner
      const cardNeg = document.getElementById('cardNeg');
      const cardPos = document.getElementById('cardPos');
      if (step === 1) {
        cardPos.style.transform = 'translateY(-2px)';
        cardPos.style.boxShadow = '0 3px 8px rgba(37,99,235,0.18)';
        cardNeg.style.transform = 'none';
        cardNeg.style.boxShadow = 'none';
      } else if (step === 2) {
        cardNeg.style.transform = 'translateY(-2px)';
        cardNeg.style.boxShadow = '0 3px 8px rgba(234,88,12,0.18)';
        cardPos.style.transform = 'none';
        cardPos.style.boxShadow = 'none';
      } else {
        cardPos.style.transform = 'none';
        cardPos.style.boxShadow = 'none';
        cardNeg.style.transform = 'none';
        cardNeg.style.boxShadow = 'none';
      }
    }

    function togglePlay() {
      const playBtn = document.getElementById('playBtn');
      if (timer) {
        clearInterval(timer);
        timer = null;
        playBtn.textContent = '▶ Play';
      } else {
        playBtn.textContent = '⏸ Pause';
        timer = setInterval(() => {
          const next = (currentStep + 1) % 3;
          setStep(next);
        }, 2200);
      }
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Integer Division Model</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 8px;
      user-select: none;
    }

    .header {
      text-align: center;
      margin-bottom: 8px;
    }

    .question-badge {
      display: inline-block;
      background: #eff6ff;
      color: #1d4ed8;
      border: 1px solid #bfdbfe;
      font-size: 14px;
      font-weight: 600;
      padding: 4px 12px;
      border-radius: 16px;
    }

    .stage {
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 8px;
      width: 100%;
      max-width: 500px;
      padding: 4px 0;
    }

    .set-column {
      display: flex;
      flex-direction: column;
      align-items: center;
      background: #f8fafc;
      border: 2px dashed #3b82f6;
      border-radius: 20px;
      padding: 8px 6px;
      gap: 6px;
      flex: 1;
      max-width: 100px;
      transition: background-color 0.25s ease, border-color 0.25s ease, transform 0.25s ease;
      cursor: pointer;
    }

    .set-column.active {
      background: #dbeafe;
      border-color: #1d4ed8;
      box-shadow: 0 0 0 2px #93c5fd;
    }

    .set-tag {
      font-size: 12px;
      font-weight: 700;
      color: #1d4ed8;
      letter-spacing: 0.2px;
    }

    .chip-stack {
      display: flex;
      flex-direction: column;
      gap: 6px;
      align-items: center;
    }

    .chip {
      width: 36px;
      height: 36px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #f87171, #dc2626);
      color: #ffffff;
      font-size: 14px;
      font-weight: 800;
      display: flex;
      align-items: center;
      justify-content: center;
      box-shadow: 0 2px 4px rgba(220, 38, 38, 0.25);
    }

    .sub-value {
      font-size: 11px;
      font-weight: 700;
      color: #dc2626;
      margin-top: 2px;
    }

    .count-banner {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      font-size: 14px;
      font-weight: 600;
      color: #475569;
      background: #f1f5f9;
      padding: 6px 14px;
      border-radius: 12px;
      margin: 4px 0;
    }

    .count-banner strong {
      color: #15803d;
      font-size: 16px;
    }

    .equation-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: 24px;
      font-weight: 800;
      padding: 8px 16px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 14px;
      width: 100%;
      max-width: 440px;
    }

    .num-total { color: #dc2626; }
    .num-group { color: #2563eb; }
    .num-result {
      color: #16a34a;
      background: #dcfce7;
      border: 1px solid #86efac;
      padding: 2px 10px;
      border-radius: 8px;
    }

    .symbol {
      color: #64748b;
      font-weight: 600;
    }

    @media (max-width: 380px) {
      .chip {
        width: 30px;
        height: 30px;
        font-size: 12px;
      }
      .set-tag {
        font-size: 11px;
      }
      .equation-bar {
        font-size: 20px;
        gap: 6px;
      }
      .question-badge {
        font-size: 12px;
      }
    }
  </style>
</head>
<body>

  <div class="header">
    <div class="question-badge">How many groups of −3 are in −12?</div>
  </div>

  <div class="stage">
    <div class="set-column" id="set1">
      <span class="set-tag">Set 1</span>
      <div class="chip-stack">
        <div class="chip">−1</div>
        <div class="chip">−1</div>
        <div class="chip">−1</div>
      </div>
      <span class="sub-value">−3</span>
    </div>

    <div class="set-column" id="set2">
      <span class="set-tag">Set 2</span>
      <div class="chip-stack">
        <div class="chip">−1</div>
        <div class="chip">−1</div>
        <div class="chip">−1</div>
      </div>
      <span class="sub-value">−3</span>
    </div>

    <div class="set-column" id="set3">
      <span class="set-tag">Set 3</span>
      <div class="chip-stack">
        <div class="chip">−1</div>
        <div class="chip">−1</div>
        <div class="chip">−1</div>
      </div>
      <span class="sub-value">−3</span>
    </div>

    <div class="set-column" id="set4">
      <span class="set-tag">Set 4</span>
      <div class="chip-stack">
        <div class="chip">−1</div>
        <div class="chip">−1</div>
        <div class="chip">−1</div>
      </div>
      <span class="sub-value">−3</span>
    </div>
  </div>

  <div class="count-banner">
    <span>Total: <strong>4 equal groups</strong></span>
  </div>

  <div class="equation-bar">
    <span class="num-total">−12</span>
    <span class="symbol">÷</span>
    <span class="num-group">−3</span>
    <span class="symbol">=</span>
    <span class="num-result">+4</span>
  </div>

  <script>
    const columns = document.querySelectorAll('.set-column');
    columns.forEach((col) => {
      col.addEventListener('click', () => {
        col.classList.toggle('active');
      });
    });
  </script>
</body>
</html>

Modeling Integer Division with Concrete Models

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      width: 100%;
      min-height: 100%;
      background: #ffffff;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      user-select: none;
    }

    .diagram-area {
      width: 100%;
      max-width: 440px;
      position: relative;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    /* Interactive controls */
    .controls {
      display: flex;
      flex-wrap: wrap;
      gap: 6px;
      justify-content: center;
      margin-top: 14px;
      width: 100%;
      max-width: 440px;
    }

    .btn-tab {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      border-radius: 20px;
      padding: 6px 12px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: all 0.25s ease;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }

    .btn-tab:hover {
      background: #e2e8f0;
    }

    .btn-tab.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
      box-shadow: 0 2px 6px rgba(30, 41, 69, 0.2);
    }

    /* Equation Banner */
    .formula-banner {
      min-height: 38px;
      margin-top: 10px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 17px;
      font-weight: 700;
      color: #1e2945;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 16px;
      width: 100%;
      max-width: 380px;
      text-align: center;
      transition: background 0.25s ease;
    }

    .badge-pos {
      color: #b45309;
      background: #fef3c7;
      padding: 1px 6px;
      border-radius: 4px;
      border: 1px solid #fcd34d;
    }

    .badge-neg {
      color: #b91c1c;
      background: #fee2e2;
      padding: 1px 6px;
      border-radius: 4px;
      border: 1px solid #fca5a5;
    }

    /* SVG elements transition */
    .rel-line, .rel-label, .rel-arrow {
      transition: opacity 0.3s ease, stroke 0.3s ease;
    }
  </style>
</head>
<body>

  <div class="diagram-area">
    <svg viewBox="0 0 400 310" aria-label="Math Fact Family Triangle">
      <defs>
        
        <marker id="arrow-yellow" markerWidth="8" markerHeight="8" refX="5" refY="3" orient="auto">
          <polygon points="0 0, 6 3, 0 6" fill="#d97706" />
        </marker>
        <marker id="arrow-blue" markerWidth="8" markerHeight="8" refX="5" refY="3" orient="auto">
          <polygon points="0 0, 6 3, 0 6" fill="#0284c7" />
        </marker>
        <marker id="arrow-indigo" markerWidth="8" markerHeight="8" refX="5" refY="3" orient="auto">
          <polygon points="0 0, 6 3, 0 6" fill="#6366f1" />
        </marker>
        <marker id="arrow-gray" markerWidth="8" markerHeight="8" refX="5" refY="3" orient="auto">
          <polygon points="0 0, 6 3, 0 6" fill="#94a3b8" />
        </marker>

        
        <filter id="soft-shadow" x="-10%" y="-10%" width="120%" height="120%">
          <feDropShadow dx="0" dy="2" stdDeviation="3" flood-opacity="0.08" />
        </filter>
      </defs>

      
      <polygon points="200,48 70,252 330,252" fill="#f8fafc" stroke="#e2e8f0" stroke-width="2" stroke-linejoin="round" />

      
      <g id="rel-left" class="rel-group">
        <path d="M 180,68 L 92,230" fill="none" stroke="#0284c7" stroke-width="3" stroke-dasharray="5,4" marker-end="url(#arrow-blue)" class="rel-line" />
        <g transform="translate(90, 142)">
          <rect x="-10" y="-12" width="94" height="24" rx="12" fill="#ffffff" stroke="#0284c7" stroke-width="1.5" filter="url(#soft-shadow)"/>
          <text x="37" y="4" text-anchor="middle" font-size="12" font-weight="700" fill="#0369a1">+12 ÷ (-3)</text>
        </g>
      </g>

      
      <g id="rel-right" class="rel-group">
        <path d="M 220,68 L 308,230" fill="none" stroke="#6366f1" stroke-width="3" stroke-dasharray="5,4" marker-end="url(#arrow-indigo)" class="rel-line" />
        <g transform="translate(226, 142)">
          <rect x="-10" y="-12" width="94" height="24" rx="12" fill="#ffffff" stroke="#6366f1" stroke-width="1.5" filter="url(#soft-shadow)"/>
          <text x="37" y="4" text-anchor="middle" font-size="12" font-weight="700" fill="#4338ca">+12 ÷ (-4)</text>
        </g>
      </g>

      
      <g id="rel-bottom" class="rel-group">
        <path d="M 112,252 L 288,252" fill="none" stroke="#d97706" stroke-width="3" marker-end="url(#arrow-yellow)" class="rel-line" />
        <g transform="translate(200, 276)">
          <rect x="-60" y="-12" width="120" height="24" rx="12" fill="#ffffff" stroke="#d97706" stroke-width="1.5" filter="url(#soft-shadow)"/>
          <text x="0" y="4" text-anchor="middle" font-size="12" font-weight="700" fill="#b45309">(-3) × (-4)</text>
        </g>
      </g>

      
      <g transform="translate(200, 48)">
        <circle r="32" fill="#fef08a" stroke="#ca8a04" stroke-width="2.5" filter="url(#soft-shadow)" />
        <text x="0" y="6" text-anchor="middle" font-size="20" font-weight="800" fill="#854d0e">+12</text>
        <circle cx="18" cy="-18" r="9" fill="#eab308" />
        <text x="18" y="-15" text-anchor="middle" font-size="12" font-weight="800" fill="#ffffff">+</text>
      </g>

      
      <g transform="translate(70, 252)">
        <circle r="30" fill="#fee2e2" stroke="#dc2626" stroke-width="2.5" filter="url(#soft-shadow)" />
        <text x="0" y="6" text-anchor="middle" font-size="20" font-weight="800" fill="#991b1b">-3</text>
        <circle cx="17" cy="-17" r="9" fill="#ef4444" />
        <text x="17" y="-15" text-anchor="middle" font-size="12" font-weight="800" fill="#ffffff">−</text>
      </g>

      
      <g transform="translate(330, 252)">
        <circle r="30" fill="#fee2e2" stroke="#dc2626" stroke-width="2.5" filter="url(#soft-shadow)" />
        <text x="0" y="6" text-anchor="middle" font-size="20" font-weight="800" fill="#991b1b">-4</text>
        <circle cx="17" cy="-17" r="9" fill="#ef4444" />
        <text x="17" y="-15" text-anchor="middle" font-size="12" font-weight="800" fill="#ffffff">−</text>
      </g>
    </svg>
  </div>

  
  <div id="equationBanner" class="formula-banner">
    <span class="badge-pos">+12</span> &nbsp;=&nbsp; <span class="badge-neg">-3</span> &nbsp;×&nbsp; <span class="badge-neg">-4</span>
  </div>

  
  <div class="controls">
    <button class="btn-tab active" data-mode="all">All Facts</button>
    <button class="btn-tab" data-mode="mult">(-3) × (-4)</button>
    <button class="btn-tab" data-mode="div-left">+12 ÷ (-3)</button>
    <button class="btn-tab" data-mode="div-right">+12 ÷ (-4)</button>
  </div>

  <script>
    const buttons = document.querySelectorAll('.btn-tab');
    const groupLeft = document.getElementById('rel-left');
    const groupRight = document.getElementById('rel-right');
    const groupBottom = document.getElementById('rel-bottom');
    const banner = document.getElementById('equationBanner');

    const formulas = {
      'all': '<span class="badge-pos">+12</span> &nbsp;=&nbsp; <span class="badge-neg">-3</span> &nbsp;×&nbsp; <span class="badge-neg">-4</span>',
      'mult': '(<span class="badge-neg">-3</span>) × (<span class="badge-neg">-4</span>) &nbsp;=&nbsp; <span class="badge-pos">+12</span>',
      'div-left': '<span class="badge-pos">+12</span> ÷ (<span class="badge-neg">-3</span>) &nbsp;=&nbsp; <span class="badge-neg">-4</span>',
      'div-right': '<span class="badge-pos">+12</span> ÷ (<span class="badge-neg">-4</span>) &nbsp;=&nbsp; <span class="badge-neg">-3</span>'
    };

    function setMode(mode) {
      buttons.forEach(btn => {
        btn.classList.toggle('active', btn.dataset.mode === mode);
      });

      banner.innerHTML = formulas[mode];

      if (mode === 'all') {
        groupLeft.style.opacity = '1';
        groupRight.style.opacity = '1';
        groupBottom.style.opacity = '1';
      } else if (mode === 'mult') {
        groupLeft.style.opacity = '0.15';
        groupRight.style.opacity = '0.15';
        groupBottom.style.opacity = '1';
      } else if (mode === 'div-left') {
        groupLeft.style.opacity = '1';
        groupRight.style.opacity = '0.15';
        groupBottom.style.opacity = '0.15';
      } else if (mode === 'div-right') {
        groupLeft.style.opacity = '0.15';
        groupRight.style.opacity = '1';
        groupBottom.style.opacity = '0.15';
      }
    }

    buttons.forEach(btn => {
      btn.addEventListener('click', () => setMode(btn.dataset.mode));
    });
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Integer Division Sign Rules</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      background: transparent;
      padding: 12px;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      gap: 12px;
      width: 100%;
      min-height: 100%;
      justify-content: center;
    }

    .grid-container {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
      gap: 12px;
      width: 100%;
    }

    .rule-card {
      border-radius: 12px;
      padding: 14px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      transition: box-shadow 0.2s ease;
    }

    /* Green Theme: Same Signs */
    .card-same {
      background: #f0fdf4;
      border: 2px solid #86efac;
    }

    .card-same .card-header {
      background: #16a34a;
      color: #ffffff;
    }

    .card-same .badge-res {
      background: #22c55e;
      color: #ffffff;
    }

    .card-same .row-box {
      background: #ffffff;
      border: 1px solid #bbf7d0;
    }

    .card-same .row-box.active {
      box-shadow: 0 0 0 2px #16a34a;
      background: #fcfdfd;
    }

    /* Amber Theme: Different Signs */
    .card-diff {
      background: #fffbeb;
      border: 2px solid #fde68a;
    }

    .card-diff .card-header {
      background: #d97706;
      color: #ffffff;
    }

    .card-diff .badge-res {
      background: #f59e0b;
      color: #ffffff;
    }

    .card-diff .row-box {
      background: #ffffff;
      border: 1px solid #fef3c7;
    }

    .card-diff .row-box.active {
      box-shadow: 0 0 0 2px #d97706;
      background: #fffdf9;
    }

    .card-header {
      padding: 8px 12px;
      border-radius: 8px;
      font-size: 15px;
      font-weight: 700;
      text-align: center;
      letter-spacing: 0.2px;
    }

    .rows-group {
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .row-box {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 10px 12px;
      border-radius: 8px;
      cursor: pointer;
      user-select: none;
      transition: background 0.15s ease, box-shadow 0.15s ease;
    }

    .rule-formula {
      display: flex;
      align-items: center;
      gap: 6px;
      font-size: 16px;
      font-weight: 700;
    }

    .badge-sign {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 24px;
      height: 24px;
      border-radius: 6px;
      font-size: 16px;
      font-weight: 800;
    }

    .sign-pos {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #86efac;
    }

    .sign-neg {
      background: #fee2e2;
      color: #b91c1c;
      border: 1px solid #fca5a5;
    }

    .op {
      color: #6b7280;
      font-size: 15px;
      font-weight: 600;
    }

    .badge-res {
      padding: 2px 8px;
      border-radius: 6px;
      font-size: 14px;
      font-weight: 700;
    }

    .example-math {
      font-size: 15px;
      font-weight: 700;
      color: #374151;
      letter-spacing: 0.3px;
    }

    /* Interactive Tester Bar */
    .tester-bar {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: center;
      gap: 8px;
      padding: 8px 12px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
    }

    .tester-label {
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
    }

    .test-btn {
      background: #ffffff;
      border: 1.5px solid #cbd5e1;
      border-radius: 6px;
      padding: 4px 10px;
      font-size: 14px;
      font-weight: 700;
      cursor: pointer;
      color: #1e2945;
      transition: background 0.15s ease;
    }

    .test-btn:active {
      background: #e2e8f0;
    }

    .display-eq {
      font-size: 16px;
      font-weight: 800;
      padding: 4px 10px;
      border-radius: 6px;
      background: #ffffff;
      border: 1.5px solid #cbd5e1;
      color: #1e2945;
      min-width: 140px;
      text-align: center;
    }
  </style>
</head>
<body>

  <div class="grid-container">
    
    <div class="rule-card card-same">
      <div class="card-header">Same Signs → Positive (+)</div>
      <div class="rows-group">
        <div class="row-box" onclick="selectRule(15, 3, true)" id="row-0">
          <div class="rule-formula">
            <span class="badge-sign sign-pos">+</span>
            <span class="op">÷</span>
            <span class="badge-sign sign-pos">+</span>
            <span class="op">=</span>
            <span class="badge-res">+</span>
          </div>
          <div class="example-math">15 ÷ 3 = 5</div>
        </div>

        <div class="row-box" onclick="selectRule(-15, -3, true)" id="row-1">
          <div class="rule-formula">
            <span class="badge-sign sign-neg">−</span>
            <span class="op">÷</span>
            <span class="badge-sign sign-neg">−</span>
            <span class="op">=</span>
            <span class="badge-res">+</span>
          </div>
          <div class="example-math">−15 ÷ −3 = 5</div>
        </div>
      </div>
    </div>

    
    <div class="rule-card card-diff">
      <div class="card-header">Different Signs → Negative (−)</div>
      <div class="rows-group">
        <div class="row-box" onclick="selectRule(-15, 3, false)" id="row-2">
          <div class="rule-formula">
            <span class="badge-sign sign-neg">−</span>
            <span class="op">÷</span>
            <span class="badge-sign sign-pos">+</span>
            <span class="op">=</span>
            <span class="badge-res">−</span>
          </div>
          <div class="example-math">−15 ÷ 3 = −5</div>
        </div>

        <div class="row-box" onclick="selectRule(15, -3, false)" id="row-3">
          <div class="rule-formula">
            <span class="badge-sign sign-pos">+</span>
            <span class="op">÷</span>
            <span class="badge-sign sign-neg">−</span>
            <span class="op">=</span>
            <span class="badge-res">−</span>
          </div>
          <div class="example-math">15 ÷ −3 = −5</div>
        </div>
      </div>
    </div>
  </div>

  
  <div class="tester-bar">
    <span class="tester-label">Interactive:</span>
    <button class="test-btn" onclick="toggleNumerator()">Toggle Numerator</button>
    <button class="test-btn" onclick="toggleDenominator()">Toggle Denominator</button>
    <div class="display-eq" id="displayEq">15 ÷ 3 = 5</div>
  </div>

  <script>
    let num = 15;
    let den = 3;

    function updateView() {
      const res = num / den;
      const numStr = num < 0 ? `−${Math.abs(num)}` : `${num}`;
      const denStr = den < 0 ? `−${Math.abs(den)}` : `${den}`;
      const resStr = res < 0 ? `−${Math.abs(res)}` : `${res}`;
      
      const display = document.getElementById('displayEq');
      display.textContent = `${numStr} ÷ ${denStr} = ${resStr}`;

      const isSame = (num > 0 && den > 0) || (num < 0 && den < 0);
      if (isSame) {
        display.style.borderColor = '#86efac';
        display.style.color = '#15803d';
        display.style.background = '#f0fdf4';
      } else {
        display.style.borderColor = '#fde68a';
        display.style.color = '#b45309';
        display.style.background = '#fffbeb';
      }

      // Highlight corresponding row
      for (let i = 0; i < 4; i++) {
        const el = document.getElementById(`row-${i}`);
        if (el) el.classList.remove('active');
      }

      if (num > 0 && den > 0) document.getElementById('row-0').classList.add('active');
      else if (num < 0 && den < 0) document.getElementById('row-1').classList.add('active');
      else if (num < 0 && den > 0) document.getElementById('row-2').classList.add('active');
      else if (num > 0 && den < 0) document.getElementById('row-3').classList.add('active');
    }

    function toggleNumerator() {
      num = -num;
      updateView();
    }

    function toggleDenominator() {
      den = -den;
      updateView();
    }

    function selectRule(n, d) {
      num = n;
      den = d;
      updateView();
    }

    // Initialize first row active
    updateView();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Modeling Integer Division: -12 ÷ 3</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      background-color: #f8f9fa;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 14px;
      user-select: none;
    }

    .main-stage {
      width: 100%;
      max-width: 540px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      flex: 1;
      justify-content: space-between;
    }

    /* Top Section: Pool */
    .pool-section {
      background: #ffffff;
      border: 1.5px dashed #cbd5e1;
      border-radius: 12px;
      padding: 8px 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      min-height: 84px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
    }

    .section-label {
      font-size: 13px;
      font-weight: 700;
      color: #475569;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .chips-grid {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 6px;
      width: 100%;
      min-height: 38px;
      align-items: center;
    }

    /* Chip Styling */
    .chip {
      width: 32px;
      height: 32px;
      background: #ef4444;
      color: #ffffff;
      border-radius: 50%;
      font-size: 13px;
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
      box-shadow: 0 2px 4px rgba(239, 68, 68, 0.28);
      transition: all 0.4s cubic-bezier(0.34, 1.3, 0.64, 1);
    }

    .chip.placeholder {
      background: transparent;
      border: 1.5px dashed #e2e8f0;
      color: transparent;
      box-shadow: none;
    }

    /* Groups Section */
    .groups-container {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 10px;
      width: 100%;
    }

    .group-box {
      background: #ffffff;
      border: 2px solid #3b82f6;
      border-radius: 12px;
      padding: 8px 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      min-height: 108px;
      box-shadow: 0 2px 6px rgba(59, 130, 246, 0.08);
      transition: border-color 0.3s ease;
    }

    .group-title {
      font-size: 13px;
      font-weight: 700;
      color: #1e40af;
    }

    .group-chips {
      display: grid;
      grid-template-columns: repeat(2, 32px);
      grid-template-rows: repeat(2, 32px);
      gap: 6px;
      justify-content: center;
      align-content: center;
      min-height: 70px;
    }

    /* Bottom Highlight Banner */
    .banner {
      background: #eff6ff;
      border: 1.5px solid #bfdbfe;
      border-radius: 10px;
      padding: 8px 12px;
      text-align: center;
      display: flex;
      flex-direction: column;
      gap: 2px;
    }

    .banner-text {
      font-size: 13px;
      font-weight: 600;
      color: #1e3a8a;
    }

    .banner-equation {
      font-size: 18px;
      font-weight: 800;
      color: #1d4ed8;
      letter-spacing: 0.5px;
    }

    /* Controls */
    .controls {
      display: flex;
      gap: 8px;
      justify-content: center;
      width: 100%;
    }

    .btn {
      appearance: none;
      border: none;
      background: #3b82f6;
      color: #ffffff;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 5px;
      transition: background 0.2s ease, opacity 0.2s ease;
    }

    .btn:hover {
      background: #2563eb;
    }

    .btn-secondary {
      background: #e2e8f0;
      color: #334155;
    }

    .btn-secondary:hover {
      background: #cbd5e1;
    }
  </style>
</head>
<body>

  <div class="main-stage">
    
    <div class="pool-section">
      <div class="section-label" id="poolLabel">Total: -12</div>
      <div class="chips-grid" id="poolGrid"></div>
    </div>

    
    <div class="groups-container">
      <div class="group-box">
        <div class="group-title">Group 1</div>
        <div class="group-chips" id="group0"></div>
      </div>
      <div class="group-box">
        <div class="group-title">Group 2</div>
        <div class="group-chips" id="group1"></div>
      </div>
      <div class="group-box">
        <div class="group-title">Group 3</div>
        <div class="group-chips" id="group2"></div>
      </div>
    </div>

    
    <div class="banner">
      <div class="banner-text" id="bannerDesc">Distribute -12 into 3 equal groups</div>
      <div class="banner-equation" id="bannerEq">-12 ÷ 3 = ?</div>
    </div>

    
    <div class="controls">
      <button class="btn" id="actionBtn">▶ Distribute</button>
      <button class="btn btn-secondary" id="resetBtn">↺ Reset</button>
    </div>
  </div>

  <script>
    const TOTAL_CHIPS = 12;
    const NUM_GROUPS = 3;
    const CHIPS_PER_GROUP = TOTAL_CHIPS / NUM_GROUPS;

    const poolGrid = document.getElementById('poolGrid');
    const groupGrids = [
      document.getElementById('group0'),
      document.getElementById('group1'),
      document.getElementById('group2')
    ];
    const poolLabel = document.getElementById('poolLabel');
    const bannerDesc = document.getElementById('bannerDesc');
    const bannerEq = document.getElementById('bannerEq');
    const actionBtn = document.getElementById('actionBtn');
    const resetBtn = document.getElementById('resetBtn');

    let state = 'initial'; // 'initial', 'animating', 'distributed'
    let timer = null;

    function renderInitial() {
      clearTimeout(timer);
      state = 'initial';
      actionBtn.disabled = false;
      actionBtn.textContent = '▶ Distribute';
      
      poolLabel.textContent = 'Total: -12';
      bannerDesc.textContent = 'Distribute -12 into 3 equal groups';
      bannerEq.textContent = '-12 ÷ 3 = ?';

      poolGrid.innerHTML = '';
      for (let i = 0; i < TOTAL_CHIPS; i++) {
        const chip = document.createElement('div');
        chip.className = 'chip';
        chip.id = 'pool-chip-' + i;
        chip.textContent = '-1';
        poolGrid.appendChild(chip);
      }

      groupGrids.forEach(g => {
        g.innerHTML = '';
        for (let i = 0; i < CHIPS_PER_GROUP; i++) {
          const placeholder = document.createElement('div');
          placeholder.className = 'chip placeholder';
          g.appendChild(placeholder);
        }
      });
    }

    function distribute() {
      if (state === 'animating') return;
      if (state === 'distributed') {
        renderInitial();
        return;
      }

      state = 'animating';
      actionBtn.disabled = true;

      let distributedCount = 0;

      function step() {
        if (distributedCount >= TOTAL_CHIPS) {
          state = 'distributed';
          actionBtn.disabled = false;
          actionBtn.textContent = '↺ Reset';
          poolLabel.textContent = 'Total: 0 remaining';
          bannerDesc.textContent = 'Each group gets 4 red counters = -4';
          bannerEq.textContent = '-12 ÷ 3 = -4';
          return;
        }

        const targetGroupIdx = distributedCount % NUM_GROUPS;
        const targetSlotIdx = Math.floor(distributedCount / NUM_GROUPS);

        // Hide one chip from top
        const poolChip = document.getElementById('pool-chip-' + (TOTAL_CHIPS - 1 - distributedCount));
        if (poolChip) {
          poolChip.style.visibility = 'hidden';
          poolChip.style.opacity = '0';
        }

        // Fill one chip in target group
        const targetBox = groupGrids[targetGroupIdx];
        const placeholder = targetBox.children[targetSlotIdx];
        if (placeholder) {
          placeholder.className = 'chip';
          placeholder.textContent = '-1';
          placeholder.style.transform = 'scale(1.2)';
          setTimeout(() => {
            placeholder.style.transform = 'scale(1)';
          }, 150);
        }

        distributedCount++;
        const remaining = TOTAL_CHIPS - distributedCount;
        poolLabel.textContent = remaining > 0 ? `Remaining: -${remaining}` : 'Total: 0';

        timer = setTimeout(step, 240);
      }

      step();
    }

    actionBtn.addEventListener('click', () => {
      if (state === 'initial') {
        distribute();
      } else if (state === 'distributed') {
        renderInitial();
      }
    });

    resetBtn.addEventListener('click', renderInitial);

    // Initial render
    renderInitial();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 10px;
      min-height: 100%;
    }

    .diagram-content {
      width: 100%;
      max-width: 600px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
    }

    /* Controls / Stepper */
    .step-controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 20px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: background 0.2s, color 0.2s, border-color 0.2s, box-shadow 0.2s;
    }

    .step-btn:hover {
      background: #e2e8f0;
    }

    .step-btn.active {
      background: #ff5757;
      border-color: #ff5757;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(255, 87, 87, 0.35);
    }

    /* SVG Canvas */
    .svg-container {
      width: 100%;
      display: flex;
      justify-content: center;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    /* SVG Elements */
    .axis-line {
      stroke: #64748b;
      stroke-width: 2.5;
      stroke-linecap: round;
    }

    .tick-line {
      stroke: #94a3b8;
      stroke-width: 1.5;
    }

    .tick-line.major {
      stroke: #475569;
      stroke-width: 2.2;
    }

    .tick-label {
      font-size: 16px;
      font-weight: 700;
      fill: #64748b;
      text-anchor: middle;
      user-select: none;
    }

    .tick-label.highlight-start {
      fill: #0284c7;
      font-size: 18px;
      font-weight: 800;
    }

    .tick-label.highlight-end {
      fill: #ff5757;
      font-size: 18px;
      font-weight: 800;
    }

    .jump-arc {
      fill: none;
      stroke: #ff5757;
      stroke-width: 3.5;
      stroke-linecap: round;
      transition: opacity 0.3s ease;
    }

    .jump-badge-rect {
      fill: #ff5757;
      rx: 11;
      ry: 11;
    }

    .jump-badge-text {
      fill: #ffffff;
      font-size: 14px;
      font-weight: 800;
      text-anchor: middle;
      dominant-baseline: central;
    }

    .jump-group {
      opacity: 0.15;
      transition: opacity 0.3s ease;
    }

    .jump-group.visible {
      opacity: 1;
    }

    /* Equations Section */
    .equations-panel {
      width: 100%;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .eq-row {
      display: flex;
      align-items: center;
      justify-content: center;
      flex-wrap: wrap;
      gap: 6px 10px;
      background: #f8fafc;
      border-radius: 8px;
      padding: 8px 12px;
      font-size: 15px;
      font-weight: 700;
      color: #334155;
      text-align: center;
    }

    .eq-label {
      color: #64748b;
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .eq-math {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      flex-wrap: wrap;
      justify-content: center;
    }

    .eq-pill {
      display: inline-flex;
      align-items: center;
      padding: 2px 7px;
      border-radius: 6px;
      background: #e2e8f0;
      color: #64748b;
      font-size: 14px;
      transition: all 0.3s ease;
    }

    .eq-pill.active {
      background: #fee2e2;
      color: #e11d48;
      border: 1px solid #fca5a5;
    }

    .eq-result {
      color: #ff5757;
      font-size: 16px;
      font-weight: 800;
    }

    .mult-factor {
      color: #0284c7;
      font-size: 16px;
      font-weight: 800;
    }

    @media (max-width: 420px) {
      .eq-row {
        flex-direction: column;
        gap: 4px;
        padding: 6px 8px;
      }
      .eq-label {
        font-size: 12px;
      }
      .eq-math {
        font-size: 14px;
      }
    }
  </style>
</head>
<body>

  <div class="diagram-content">
    
    <div class="step-controls">
      <button class="step-btn" data-step="1">1 Jump</button>
      <button class="step-btn" data-step="2">2 Jumps</button>
      <button class="step-btn active" data-step="3">All 3 Jumps</button>
    </div>

    
    <div class="svg-container">
      <svg viewBox="0 0 600 175">
        <defs>
          <marker id="arrow-left" viewBox="0 0 10 10" refX="2" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 8 1 L 2 5 L 8 9 z" fill="#ff5757" />
          </marker>
          <marker id="axis-arr-l" viewBox="0 0 10 10" refX="2" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 8 1 L 2 5 L 8 9 z" fill="#64748b" />
          </marker>
          <marker id="axis-arr-r" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 2 1 L 8 5 L 2 9 z" fill="#64748b" />
          </marker>
        </defs>

        
        <line x1="20" y1="110" x2="580" y2="110" class="axis-line" marker-start="url(#axis-arr-l)" marker-end="url(#axis-arr-r)" />

        
        
        <line x1="30" y1="100" x2="30" y2="120" class="tick-line major" />
        <text x="30" y="145" class="tick-label">-14</text>

        
        <line x1="63.75" y1="104" x2="63.75" y2="116" class="tick-line" />

        
        <line x1="97.5" y1="98" x2="97.5" y2="122" class="tick-line major" stroke="#ff5757" stroke-width="2.5" />
        <text x="97.5" y="145" class="tick-label highlight-end">-12</text>

        
        <line x1="131.25" y1="104" x2="131.25" y2="116" class="tick-line" />

        
        <line x1="165" y1="100" x2="165" y2="120" class="tick-line major" />
        <text x="165" y="145" class="tick-label">-10</text>

        
        <line x1="198.75" y1="104" x2="198.75" y2="116" class="tick-line" />

        
        <line x1="232.5" y1="100" x2="232.5" y2="120" class="tick-line major" />
        <text x="232.5" y="145" class="tick-label">-8</text>

        
        <line x1="266.25" y1="104" x2="266.25" y2="116" class="tick-line" />

        
        <line x1="300" y1="100" x2="300" y2="120" class="tick-line major" />
        <text x="300" y="145" class="tick-label">-6</text>

        
        <line x1="333.75" y1="104" x2="333.75" y2="116" class="tick-line" />

        
        <line x1="367.5" y1="100" x2="367.5" y2="120" class="tick-line major" />
        <text x="367.5" y="145" class="tick-label">-4</text>

        
        <line x1="401.25" y1="104" x2="401.25" y2="116" class="tick-line" />

        
        <line x1="435" y1="100" x2="435" y2="120" class="tick-line major" />
        <text x="435" y="145" class="tick-label">-2</text>

        
        <line x1="468.75" y1="104" x2="468.75" y2="116" class="tick-line" />

        
        <line x1="502.5" y1="98" x2="502.5" y2="122" class="tick-line major" stroke="#0284c7" stroke-width="2.5" />
        <text x="502.5" y="145" class="tick-label highlight-start">0</text>

        
        <line x1="536.25" y1="104" x2="536.25" y2="116" class="tick-line" />

        
        <line x1="570" y1="100" x2="570" y2="120" class="tick-line major" />
        <text x="570" y="145" class="tick-label">2</text>

        
        <g id="jump-1" class="jump-group visible">
          <path d="M 502.5 105 Q 435 25 371.5 105" class="jump-arc" marker-end="url(#arrow-left)" />
          <rect x="417" y="31" width="36" height="22" class="jump-badge-rect" />
          <text x="435" y="42" class="jump-badge-text">-4</text>
        </g>

        
        <g id="jump-2" class="jump-group visible">
          <path d="M 367.5 105 Q 300 25 236.5 105" class="jump-arc" marker-end="url(#arrow-left)" />
          <rect x="282" y="31" width="36" height="22" class="jump-badge-rect" />
          <text x="300" y="42" class="jump-badge-text">-4</text>
        </g>

        
        <g id="jump-3" class="jump-group visible">
          <path d="M 232.5 105 Q 165 25 101.5 105" class="jump-arc" marker-end="url(#arrow-left)" />
          <rect x="147" y="31" width="36" height="22" class="jump-badge-rect" />
          <text x="165" y="42" class="jump-badge-text">-4</text>
        </g>

        
        <circle id="end-marker" cx="97.5" cy="110" r="6" fill="#ff5757" stroke="#ffffff" stroke-width="2" />

        
        <circle cx="502.5" cy="110" r="6" fill="#0284c7" stroke="#ffffff" stroke-width="2" />
      </svg>
    </div>

    
    <div class="equations-panel">
      
      <div class="eq-row">
        <span class="eq-label">Repeated Addition:</span>
        <div class="eq-math">
          <span class="eq-pill active" id="add-1">(-4)</span>
          <span id="plus-1">+</span>
          <span class="eq-pill active" id="add-2">(-4)</span>
          <span id="plus-2">+</span>
          <span class="eq-pill active" id="add-3">(-4)</span>
          <span>=</span>
          <span class="eq-result" id="eq-sum">-12</span>
        </div>
      </div>

      
      <div class="eq-row">
        <span class="eq-label">Multiplication:</span>
        <div class="eq-math">
          <span class="mult-factor" id="mult-count">3</span>
          <span>×</span>
          <span class="eq-pill active" id="mult-val">(-4)</span>
          <span>=</span>
          <span class="eq-result" id="eq-prod">-12</span>
        </div>
      </div>
    </div>
  </div>

  <script>
    const buttons = document.querySelectorAll('.step-btn');
    const jumps = [
      document.getElementById('jump-1'),
      document.getElementById('jump-2'),
      document.getElementById('jump-3')
    ];

    const addPills = [
      document.getElementById('add-1'),
      document.getElementById('add-2'),
      document.getElementById('add-3')
    ];

    const plusSigns = [
      document.getElementById('plus-1'),
      document.getElementById('plus-2')
    ];

    const eqSum = document.getElementById('eq-sum');
    const eqProd = document.getElementById('eq-prod');
    const multCount = document.getElementById('mult-count');
    const endMarker = document.getElementById('end-marker');

    function setStep(step) {
      // Button states
      buttons.forEach(btn => {
        btn.classList.toggle('active', parseInt(btn.dataset.step) === step);
      });

      // Jump visibility
      jumps.forEach((jump, i) => {
        jump.classList.toggle('visible', i < step);
      });

      // Addition pills & signs
      addPills.forEach((pill, i) => {
        pill.classList.toggle('active', i < step);
        pill.style.opacity = i < step ? '1' : '0.25';
      });

      plusSigns[0].style.opacity = step >= 2 ? '1' : '0.25';
      plusSigns[1].style.opacity = step >= 3 ? '1' : '0.25';

      // Values update
      const total = step * -4;
      eqSum.textContent = total;
      eqProd.textContent = total;
      multCount.textContent = step;

      // Update Landing Marker position
      const landingX = 502.5 - (step * 4 * 33.75);
      endMarker.setAttribute('cx', landingX);
    }

    buttons.forEach(btn => {
      btn.addEventListener('click', () => {
        setStep(parseInt(btn.dataset.step));
      });
    });
  </script>
</body>
</html>

Modeling Integer Multiplication with Number Lines

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Multiplying by a Negative Integer</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: transparent;
      color: #1e293b;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      padding: 12px 8px;
      user-select: none;
    }

    .container {
      width: 100%;
      max-width: 640px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }

    .header {
      text-align: center;
      width: 100%;
    }

    .title {
      font-size: 15px;
      font-weight: 700;
      color: #0f172a;
      letter-spacing: -0.01em;
    }

    .expression-box {
      margin-top: 6px;
      font-size: 19px;
      font-weight: 800;
      color: #1d4ed8;
      background: #eff6ff;
      border: 1.5px solid #93c5fd;
      border-radius: 8px;
      padding: 5px 16px;
      display: inline-block;
      min-height: 38px;
      line-height: 26px;
      transition: all 0.25s ease;
    }

    .stage {
      width: 100%;
      position: relative;
      background: transparent;
      border: none;
      box-shadow: none;
      padding: 0;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    /* Jump styling - higher inactive opacity for clear legibility */
    .jump-group {
      opacity: 0.42;
      transition: opacity 0.3s ease;
    }

    .jump-group.active {
      opacity: 1;
    }

    .jump-path {
      fill: none;
      stroke: #2563eb;
      stroke-width: 3.5;
      stroke-linecap: round;
      stroke-dasharray: 6 3;
    }

    .jump-label {
      font-size: 15px;
      font-weight: 800;
      fill: #1d4ed8;
      text-anchor: middle;
    }

    .jump-count {
      font-size: 13px;
      font-weight: 700;
      fill: #475569;
      text-anchor: middle;
    }

    /* Number line styling */
    .axis-line {
      stroke: #1e293b;
      stroke-width: 2.5;
      stroke-linecap: round;
    }

    .tick {
      stroke: #64748b;
      stroke-width: 1.5;
    }

    .tick-major {
      stroke: #1e293b;
      stroke-width: 2.5;
    }

    .tick-label {
      font-size: 14.5px;
      font-weight: 600;
      fill: #334155;
      text-anchor: middle;
      font-family: inherit;
    }

    .tick-label.target {
      fill: #dc2626;
      font-weight: 800;
    }

    .tick-label.origin {
      fill: #059669;
      font-weight: 800;
    }

    /* Marker points */
    .dot-origin {
      fill: #059669;
    }

    .dot-target {
      fill: #dc2626;
      opacity: 0;
      transition: opacity 0.3s ease;
    }

    .dot-target.active {
      opacity: 1;
    }

    .pulse-ring {
      fill: none;
      stroke: #dc2626;
      stroke-width: 2.5;
      opacity: 0;
      transform-origin: 130px 120px;
    }

    .pulse-ring.active {
      animation: pulse 1.8s infinite ease-out;
    }

    @keyframes pulse {
      0% {
        r: 6;
        opacity: 0.85;
      }
      100% {
        r: 22;
        opacity: 0;
      }
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
      width: 100%;
      margin-top: 4px;
    }

    .btn {
      appearance: none;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #334155;
      font-size: 13px;
      font-weight: 600;
      padding: 7px 14px;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
    }

    .btn:hover {
      border-color: #94a3b8;
      background: #f8fafc;
    }

    .btn:active {
      background: #f1f5f9;
    }

    .btn-step.active {
      background: #2563eb;
      border-color: #2563eb;
      color: #ffffff;
    }

    .btn-play {
      background: #0f172a;
      border-color: #0f172a;
      color: #ffffff;
      min-width: 80px;
    }

    .btn-play:hover {
      background: #1e293b;
      border-color: #1e293b;
      color: #ffffff;
    }

    @media (max-width: 480px) {
      .title {
        font-size: 14px;
      }
      .expression-box {
        font-size: 17px;
        padding: 4px 12px;
      }
      .btn {
        padding: 6px 10px;
        font-size: 12px;
      }
      .btn-play {
        min-width: 70px;
      }
    }
  </style>
</head>
<body>

  <div class="container">
    <div class="header">
      <div class="title">Multiplying by a Negative Integer</div>
      <div id="equation" class="expression-box">4 jumps of -2 = -8</div>
    </div>

    <div class="stage">
      <svg viewBox="10 25 560 138" aria-label="Number line showing 4 jumps of negative 2 to negative 8">
        <defs>
          <marker id="arrow" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
            <path d="M 10 2 L 0 5 L 10 8 z" fill="#2563eb"/>
          </marker>
          <marker id="axis-arrow-left" viewBox="0 0 10 10" refX="2" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 8 2 L 2 5 L 8 8" fill="none" stroke="#1e293b" stroke-width="2.2" stroke-linecap="round"/>
          </marker>
          <marker id="axis-arrow-right" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 2 2 L 8 5 L 2 8" fill="none" stroke="#1e293b" stroke-width="2.2" stroke-linecap="round"/>
          </marker>
        </defs>

        
        <g id="jump-1" class="jump-group">
          <path class="jump-path" d="M 530,120 Q 480,35 430,120" marker-end="url(#arrow)"/>
          <text x="480" y="58" class="jump-label">-2</text>
          <text x="480" y="74" class="jump-count">Jump 1</text>
        </g>

        
        <g id="jump-2" class="jump-group">
          <path class="jump-path" d="M 430,120 Q 380,35 330,120" marker-end="url(#arrow)"/>
          <text x="380" y="58" class="jump-label">-2</text>
          <text x="380" y="74" class="jump-count">Jump 2</text>
        </g>

        
        <g id="jump-3" class="jump-group">
          <path class="jump-path" d="M 330,120 Q 280,35 230,120" marker-end="url(#arrow)"/>
          <text x="280" y="58" class="jump-label">-2</text>
          <text x="280" y="74" class="jump-count">Jump 3</text>
        </g>

        
        <g id="jump-4" class="jump-group">
          <path class="jump-path" d="M 230,120 Q 180,35 130,120" marker-end="url(#arrow)"/>
          <text x="180" y="58" class="jump-label">-2</text>
          <text x="180" y="74" class="jump-count">Jump 4</text>
        </g>

        
        <line x1="22" y1="120" x2="558" y2="120" class="axis-line" marker-start="url(#axis-arrow-left)" marker-end="url(#axis-arrow-right)"/>

        
        
        <line x1="30" y1="112" x2="30" y2="128" class="tick-major"/>
        <text x="30" y="148" class="tick-label">-10</text>

        
        <line x1="80" y1="115" x2="80" y2="125" class="tick"/>
        <text x="80" y="148" class="tick-label">-9</text>

        
        <line x1="130" y1="112" x2="130" y2="128" class="tick-major"/>
        <text x="130" y="148" class="tick-label target">-8</text>

        
        <line x1="180" y1="115" x2="180" y2="125" class="tick"/>
        <text x="180" y="148" class="tick-label">-7</text>

        
        <line x1="230" y1="112" x2="230" y2="128" class="tick-major"/>
        <text x="230" y="148" class="tick-label">-6</text>

        
        <line x1="280" y1="115" x2="280" y2="125" class="tick"/>
        <text x="280" y="148" class="tick-label">-5</text>

        
        <line x1="330" y1="112" x2="330" y2="128" class="tick-major"/>
        <text x="330" y="148" class="tick-label">-4</text>

        
        <line x1="380" y1="115" x2="380" y2="125" class="tick"/>
        <text x="380" y="148" class="tick-label">-3</text>

        
        <line x1="430" y1="112" x2="430" y2="128" class="tick-major"/>
        <text x="430" y="148" class="tick-label">-2</text>

        
        <line x1="480" y1="115" x2="480" y2="125" class="tick"/>
        <text x="480" y="148" class="tick-label">-1</text>

        
        <line x1="530" y1="112" x2="530" y2="128" class="tick-major"/>
        <text x="530" y="148" class="tick-label origin">0</text>

        
        <circle cx="530" cy="120" r="5.5" class="dot-origin"/>

        
        <circle id="pulse-circle" cx="130" cy="120" r="6" class="pulse-ring"/>
        <circle id="target-circle" cx="130" cy="120" r="5.5" class="dot-target"/>
      </svg>
    </div>

    <div class="controls">
      <button class="btn btn-step" data-step="1">Step 1</button>
      <button class="btn btn-step" data-step="2">Step 2</button>
      <button class="btn btn-step" data-step="3">Step 3</button>
      <button class="btn btn-step" data-step="4">Step 4</button>
      <button id="playBtn" class="btn btn-play">⏸ Pause</button>
    </div>
  </div>

  <script>
    const stepsData = [
      { text: "1 jump of -2 = -2", activeJumps: 1, isFinal: false },
      { text: "2 jumps of -2 = -4", activeJumps: 2, isFinal: false },
      { text: "3 jumps of -2 = -6", activeJumps: 3, isFinal: false },
      { text: "4 jumps of -2 = -8", activeJumps: 4, isFinal: true }
    ];

    let currentStep = 0;
    let isPlaying = true;
    let timer = null;

    const eqEl = document.getElementById('equation');
    const jumpEls = [
      document.getElementById('jump-1'),
      document.getElementById('jump-2'),
      document.getElementById('jump-3'),
      document.getElementById('jump-4')
    ];
    const targetDot = document.getElementById('target-circle');
    const pulseDot = document.getElementById('pulse-circle');
    const stepBtns = document.querySelectorAll('.btn-step');
    const playBtn = document.getElementById('playBtn');

    function render(stepIdx) {
      currentStep = stepIdx;
      const data = stepsData[stepIdx];

      eqEl.textContent = data.text;

      jumpEls.forEach((el, i) => {
        if (i < data.activeJumps) {
          el.classList.add('active');
        } else {
          el.classList.remove('active');
        }
      });

      if (data.isFinal) {
        targetDot.classList.add('active');
        pulseDot.classList.add('active');
        eqEl.style.background = '#dbeafe';
        eqEl.style.borderColor = '#2563eb';
      } else {
        targetDot.classList.remove('active');
        pulseDot.classList.remove('active');
        eqEl.style.background = '#eff6ff';
        eqEl.style.borderColor = '#93c5fd';
      }

      stepBtns.forEach((btn, i) => {
        if (i === stepIdx) {
          btn.classList.add('active');
        } else {
          btn.classList.remove('active');
        }
      });
    }

    function nextStep() {
      const next = (currentStep + 1) % stepsData.length;
      render(next);
    }

    function startAutoPlay() {
      if (timer) clearInterval(timer);
      timer = setInterval(nextStep, 3000);
      isPlaying = true;
      playBtn.textContent = '⏸ Pause';
    }

    function stopAutoPlay() {
      if (timer) clearInterval(timer);
      isPlaying = false;
      playBtn.textContent = '▶ Play';
    }

    stepBtns.forEach((btn, idx) => {
      btn.addEventListener('click', () => {
        render(idx);
        stopAutoPlay();
      });
    });

    playBtn.addEventListener('click', () => {
      if (isPlaying) {
        stopAutoPlay();
      } else {
        nextStep();
        startAutoPlay();
      }
    });

    // Initialize
    render(0);
    startAutoPlay();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      color: #1e2945;
      background: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 16px;
      min-height: 100%;
    }

    .diagram-content {
      width: 100%;
      max-width: 600px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 16px;
    }

    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }

    .jump-path {
      fill: none;
      stroke: #22b7ff;
      stroke-width: 3.5;
      stroke-linecap: round;
      transition: opacity 0.3s ease, stroke 0.3s ease;
    }

    .jump-arrow {
      fill: #22b7ff;
      transition: opacity 0.3s ease, fill 0.3s ease;
    }

    .jump-badge {
      font-size: 15px;
      font-weight: 700;
      fill: #0077b6;
      transition: opacity 0.3s ease;
    }

    .jump-group {
      cursor: pointer;
      transition: transform 0.2s ease, opacity 0.3s ease;
    }

    .jump-group.dimmed {
      opacity: 0.25;
    }

    .number-text {
      font-size: 13px;
      font-weight: 600;
      fill: #64748b;
      text-anchor: middle;
      user-select: none;
    }

    .number-text.highlight {
      fill: #1e2945;
      font-weight: 800;
      font-size: 15px;
    }

    .equations-container {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 12px;
      width: 100%;
    }

    .eq-card {
      background: #f8fafc;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 18px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 4px;
      flex: 1 1 180px;
      max-width: 260px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
    }

    .eq-label {
      font-size: 12px;
      font-weight: 600;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
    }

    .eq-math {
      font-size: 20px;
      font-weight: 800;
      color: #1e2945;
    }

    .highlight-blue {
      color: #0284c7;
    }

    .controls {
      display: flex;
      gap: 8px;
      flex-wrap: wrap;
      justify-content: center;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 8px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      transition: all 0.2s ease;
    }

    .btn:hover {
      background: #e2e8f0;
    }

    .btn.active {
      background: #22b7ff;
      border-color: #0284c7;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(34, 183, 255, 0.35);
    }
  </style>
</head>
<body>
  <div class="diagram-content">
    <div class="controls">
      <button class="btn active" id="btnAll" onclick="setStep('all')">All Jumps</button>
      <button class="btn" id="btn1" onclick="setStep(1)">Jump 1 (0→4)</button>
      <button class="btn" id="btn2" onclick="setStep(2)">Jump 2 (4→8)</button>
      <button class="btn" id="btn3" onclick="setStep(3)">Jump 3 (8→12)</button>
    </div>

    
    <svg viewBox="0 0 560 170" aria-label="Number line showing 3 jumps of 4 to 12">
      <defs>
        <marker id="arrow" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#22b7ff"/>
        </marker>
        <marker id="axis-arrow-right" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 2 L 7 5 L 0 8 z" fill="#94a3b8"/>
        </marker>
        <marker id="axis-arrow-left" viewBox="0 0 10 10" refX="1" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 7 2 L 0 5 L 7 8 z" fill="#94a3b8"/>
        </marker>
      </defs>

      
      <line x1="20" y1="120" x2="540" y2="120" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round" marker-start="url(#axis-arrow-left)" marker-end="url(#axis-arrow-right)" />

      
      
      
      
      
      <g stroke="#94a3b8" stroke-width="2" stroke-linecap="round">
        <line x1="30.0" y1="112" x2="30.0" y2="128" stroke-width="2.5" stroke="#475569" />
        <line x1="65.7" y1="115" x2="65.7" y2="125" />
        <line x1="101.4" y1="115" x2="101.4" y2="125" />
        <line x1="137.1" y1="115" x2="137.1" y2="125" />
        <line x1="172.9" y1="112" x2="172.9" y2="128" stroke-width="2.5" stroke="#475569" />
        <line x1="208.6" y1="115" x2="208.6" y2="125" />
        <line x1="244.3" y1="115" x2="244.3" y2="125" />
        <line x1="280.0" y1="115" x2="280.0" y2="125" />
        <line x1="315.7" y1="112" x2="315.7" y2="128" stroke-width="2.5" stroke="#475569" />
        <line x1="351.4" y1="115" x2="351.4" y2="125" />
        <line x1="387.1" y1="115" x2="387.1" y2="125" />
        <line x1="422.9" y1="115" x2="422.9" y2="125" />
        <line x1="458.6" y1="112" x2="458.6" y2="128" stroke-width="2.5" stroke="#475569" />
        <line x1="494.3" y1="115" x2="494.3" y2="125" />
        <line x1="530.0" y1="115" x2="530.0" y2="125" />
      </g>

      
      <g>
        <text x="30.0" y="148" class="number-text highlight">0</text>
        <text x="65.7" y="146" class="number-text">1</text>
        <text x="101.4" y="146" class="number-text">2</text>
        <text x="137.1" y="146" class="number-text">3</text>
        <text x="172.9" y="148" class="number-text highlight">4</text>
        <text x="208.6" y="146" class="number-text">5</text>
        <text x="244.3" y="146" class="number-text">6</text>
        <text x="280.0" y="146" class="number-text">7</text>
        <text x="315.7" y="148" class="number-text highlight">8</text>
        <text x="351.4" y="146" class="number-text">9</text>
        <text x="387.1" y="146" class="number-text">10</text>
        <text x="422.9" y="146" class="number-text">11</text>
        <text x="458.6" y="148" class="number-text highlight">12</text>
        <text x="494.3" y="146" class="number-text">13</text>
        <text x="530.0" y="146" class="number-text">14</text>
      </g>

      
      <circle cx="458.6" cy="120" r="5" fill="#0284c7" />

      
      <g id="jump1" class="jump-group" onclick="setStep(1)">
        <path d="M 30.0 114 Q 101.4 35 170.0 112" class="jump-path" marker-end="url(#arrow)" />
        <rect x="86" y="38" width="32" height="22" rx="6" fill="#e0f2fe" />
        <text x="102" y="54" class="jump-badge" text-anchor="middle">+4</text>
      </g>

      
      <g id="jump2" class="jump-group" onclick="setStep(2)">
        <path d="M 172.9 114 Q 244.3 35 312.8 112" class="jump-path" marker-end="url(#arrow)" />
        <rect x="229" y="38" width="32" height="22" rx="6" fill="#e0f2fe" />
        <text x="245" y="54" class="jump-badge" text-anchor="middle">+4</text>
      </g>

      
      <g id="jump3" class="jump-group" onclick="setStep(3)">
        <path d="M 315.7 114 Q 387.1 35 455.7 112" class="jump-path" marker-end="url(#arrow)" />
        <rect x="372" y="38" width="32" height="22" rx="6" fill="#e0f2fe" />
        <text x="388" y="54" class="jump-badge" text-anchor="middle">+4</text>
      </g>
    </svg>

    
    <div class="equations-container">
      <div class="eq-card">
        <span class="eq-label">Repeated Addition</span>
        <span class="eq-math" id="additionText">4 + 4 + 4 = <span class="highlight-blue">12</span></span>
      </div>
      <div class="eq-card">
        <span class="eq-label">Multiplication</span>
        <span class="eq-math">3 × 4 = <span class="highlight-blue">12</span></span>
      </div>
    </div>
  </div>

  <script>
    function setStep(step) {
      const j1 = document.getElementById('jump1');
      const j2 = document.getElementById('jump2');
      const j3 = document.getElementById('jump3');
      const addText = document.getElementById('additionText');

      // Update button states
      document.getElementById('btnAll').classList.toggle('active', step === 'all');
      document.getElementById('btn1').classList.toggle('active', step === 1);
      document.getElementById('btn2').classList.toggle('active', step === 2);
      document.getElementById('btn3').classList.toggle('active', step === 3);

      if (step === 'all') {
        j1.classList.remove('dimmed');
        j2.classList.remove('dimmed');
        j3.classList.remove('dimmed');
        addText.innerHTML = '4 + 4 + 4 = <span class="highlight-blue">12</span>';
      } else if (step === 1) {
        j1.classList.remove('dimmed');
        j2.classList.add('dimmed');
        j3.classList.add('dimmed');
        addText.innerHTML = '<span class="highlight-blue">4</span>';
      } else if (step === 2) {
        j1.classList.remove('dimmed');
        j2.classList.remove('dimmed');
        j3.classList.add('dimmed');
        addText.innerHTML = '4 + 4 = <span class="highlight-blue">8</span>';
      } else if (step === 3) {
        j1.classList.remove('dimmed');
        j2.classList.remove('dimmed');
        j3.classList.remove('dimmed');
        addText.innerHTML = '4 + 4 + 4 = <span class="highlight-blue">12</span>';
      }
    }
  </script>
</body>
</html>

111.26(b)(3)(C)

Aligned learning resources

Related diagrams