<!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;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .panels {
      display: flex;
      flex-wrap: wrap;
      gap: 16px;
      width: 100%;
      max-width: 640px;
    }

    .panel {
      flex: 1 1 280px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 220px;
    }

    .panel-title {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      margin-bottom: 8px;
    }

    /* Left Panel: Number Line */
    .numline-container {
      width: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      margin: auto 0;
    }

    .numline-svg {
      width: 100%;
      height: 110px;
      overflow: visible;
    }

    /* Right Panel: Place Value */
    .pv-container {
      width: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
      margin: auto 0;
    }

    .digits-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      font-size: 26px;
      font-weight: 700;
      letter-spacing: 1px;
    }

    .digit-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-width: 32px;
    }

    .digit-val {
      padding: 4px 6px;
      border-radius: 6px;
      position: relative;
    }

    .digit-lbl {
      font-size: 11px;
      font-weight: 600;
      margin-top: 4px;
      color: #64748b;
    }

    .hundreds {
      background: #e0f2fe;
      color: #0284c7;
      box-shadow: 0 0 0 1.5px #0284c7;
    }

    .tens {
      background: #fef3c7;
      color: #d97706;
      box-shadow: 0 0 0 2px #d97706;
      border-radius: 50%;
    }

    .rule-box {
      background: #fff;
      border: 1.5px dashed #d97706;
      color: #b45309;
      font-size: 13px;
      font-weight: 700;
      padding: 6px 14px;
      border-radius: 20px;
    }

    .result-row {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 22px;
      font-weight: 800;
      color: #0f172a;
    }

    .arrow-down {
      font-size: 16px;
      color: #64748b;
    }

    .zeros {
      color: #0284c7;
      background: #e0f2fe;
      padding: 2px 6px;
      border-radius: 6px;
    }
  </style>
</head>
<body>

  <div class="panels">
    
    <div class="panel">
      <div class="panel-title">Number Line</div>
      <div class="numline-container">
        <svg class="numline-svg" viewBox="0 0 300 110">
          <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="#0284c7" />
            </marker>
          </defs>

          
          <path d="M 226 50 Q 248 18, 270 48" fill="none" stroke="#0284c7" stroke-width="2.5" stroke-dasharray="3 3" marker-end="url(#arrow)" />

          
          <line x1="20" y1="60" x2="280" y2="60" stroke="#94a3b8" stroke-width="3" stroke-linecap="round" />

          
          <line x1="30" y1="52" x2="30" y2="68" stroke="#64748b" stroke-width="2" />
          <text x="30" y="85" text-anchor="middle" font-size="12" font-weight="700" fill="#475569">14,700</text>

          
          <line x1="150" y1="50" x2="150" y2="70" stroke="#64748b" stroke-width="2" />
          <text x="150" y="85" text-anchor="middle" font-size="11" font-weight="600" fill="#64748b">14,750</text>
          <text x="150" y="98" text-anchor="middle" font-size="10" font-weight="500" fill="#94a3b8">midpoint</text>

          
          <line x1="270" y1="52" x2="270" y2="68" stroke="#0284c7" stroke-width="2.5" />
          <text x="270" y="85" text-anchor="middle" font-size="12" font-weight="800" fill="#0284c7">14,800</text>

          
          <circle cx="181.2" cy="60" r="5.5" fill="#d97706" stroke="#ffffff" stroke-width="1.5" />
          <text x="181.2" y="42" text-anchor="middle" font-size="12" font-weight="800" fill="#d97706">14,763</text>
        </svg>
      </div>
    </div>

    
    <div class="panel">
      <div class="panel-title">Place-Value Rule</div>
      <div class="pv-container">
        
        <div class="digits-row">
          <div class="digit-box">
            <span class="digit-val">14,</span>
            <span class="digit-lbl"></span>
          </div>
          <div class="digit-box">
            <span class="digit-val hundreds">7</span>
            <span class="digit-lbl" style="color: #0284c7;">Hundreds</span>
          </div>
          <div class="digit-box">
            <span class="digit-val tens">6</span>
            <span class="digit-lbl" style="color: #d97706;">Tens</span>
          </div>
          <div class="digit-box">
            <span class="digit-val">3</span>
            <span class="digit-lbl"></span>
          </div>
        </div>

        
        <div class="rule-box">
          6 ≥ 5 → Round up!
        </div>

        
        <div class="arrow-down">↓</div>

        
        <div class="result-row">
          <span>14,8</span><span class="zeros">00</span>
        </div>
      </div>
    </div>
  </div>

</body>
</html>

Rounding Multi-Digit Numbers to the Nearest 10 and 100

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Rounding Rollover Effect: 6,971</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 10px;
      user-select: none;
    }

    .main-stage {
      width: 100%;
      max-width: 460px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 14px;
    }

    /* Target Header */
    .header-row {
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .badge-tag {
      font-size: 13px;
      font-weight: 700;
      color: #7c3aed;
      background: #f5f3ff;
      border: 1px solid #ddd6fe;
      padding: 4px 12px;
      border-radius: 999px;
      letter-spacing: 0.3px;
    }

    .task-title {
      font-size: 14px;
      font-weight: 600;
      color: #64748b;
    }

    /* Place value digit grid */
    .digits-row {
      display: flex;
      gap: 8px;
      align-items: flex-end;
      position: relative;
      padding-top: 26px; /* space for carry bubble */
    }

    .digit-slot {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      width: 64px;
      position: relative;
    }

    .place-label {
      font-size: 11px;
      font-weight: 700;
      color: #64748b;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .digit-box {
      width: 64px;
      height: 72px;
      background: #ffffff;
      border: 2px solid #cbd5e1;
      border-radius: 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 34px;
      font-weight: 800;
      color: #1e293b;
      position: relative;
      transition: background-color 0.3s ease, border-color 0.3s ease, color 0.3s ease, box-shadow 0.3s ease;
      box-shadow: 0 2px 5px rgba(0,0,0,0.05);
    }

    /* Floating carry bubble */
    .carry-bubble {
      position: absolute;
      top: -24px;
      left: 50%;
      transform: translateX(-50%);
      background: #7c3aed;
      color: #ffffff;
      font-size: 12px;
      font-weight: 800;
      padding: 2px 8px;
      border-radius: 999px;
      box-shadow: 0 2px 6px rgba(124, 58, 237, 0.35);
      opacity: 0;
      visibility: hidden;
      transition: opacity 0.3s ease, transform 0.3s ease;
      z-index: 10;
      white-space: nowrap;
    }

    .carry-bubble.active {
      opacity: 1;
      visibility: visible;
      transform: translateX(-50%) translateY(-2px);
    }

    /* Step-based highlight modes */
    .highlight-target {
      border-color: #0284c7;
      background: #f0f9ff;
      color: #0369a1;
      box-shadow: 0 0 0 3px rgba(2, 132, 199, 0.2);
    }

    .highlight-look {
      border-color: #d97706;
      background: #fffbeb;
      color: #b45309;
      box-shadow: 0 0 0 3px rgba(217, 119, 6, 0.2);
    }

    .highlight-rollover {
      border-color: #8b5cf6;
      background: #f5f3ff;
      color: #6d28d9;
      box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.25);
    }

    .highlight-final {
      border-color: #10b981;
      background: #ecfdf5;
      color: #047857;
      box-shadow: 0 0 0 3px rgba(16, 185, 129, 0.22);
    }

    .zeroed {
      color: #94a3b8;
      background: #f8fafc;
      border-color: #e2e8f0;
    }

    /* Explanation & Math Action Box */
    .info-card {
      width: 100%;
      min-height: 72px;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 6px;
      text-align: center;
      box-shadow: 0 2px 5px rgba(0,0,0,0.03);
    }

    .formula-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
    }

    .pill {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      padding: 3px 10px;
      border-radius: 6px;
      font-size: 14px;
      font-weight: 700;
    }

    .pill-blue { background: #e0f2fe; color: #0369a1; }
    .pill-amber { background: #fef3c7; color: #b45309; }
    .pill-purple { background: #ede9fe; color: #6d28d9; }
    .pill-green { background: #d1fae5; color: #047857; font-size: 17px; font-weight: 800; }

    .step-desc {
      font-size: 13px;
      color: #475569;
      line-height: 1.35;
      font-weight: 500;
    }

    /* Navigation & Controls */
    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
      width: 100%;
      max-width: 460px;
      justify-content: center;
      margin-top: 4px;
    }

    .step-btn {
      flex: 1;
      padding: 8px 6px;
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 700;
      color: #475569;
      cursor: pointer;
      text-align: center;
      transition: background-color 0.2s, border-color 0.2s, color 0.2s;
    }

    .step-btn.active {
      background: #7c3aed;
      color: #ffffff;
      border-color: #7c3aed;
      box-shadow: 0 2px 6px rgba(124, 58, 237, 0.25);
    }

    .play-btn {
      width: 36px;
      height: 36px;
      flex-shrink: 0;
      border-radius: 8px;
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      font-size: 13px;
      color: #334155;
      font-weight: 700;
      transition: background-color 0.2s;
    }

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

    @media (max-width: 380px) {
      .digit-slot { width: 52px; }
      .digit-box { width: 52px; height: 62px; font-size: 28px; }
      .place-label { font-size: 10px; }
      .step-btn { font-size: 11px; padding: 7px 4px; }
      .step-desc { font-size: 12px; }
      .pill { font-size: 13px; padding: 2px 8px; }
    }
  </style>
</head>
<body>

  <div class="main-stage">
    <div class="header-row">
      <span class="task-title">Round <strong>6,971</strong> to:</span>
      <span class="badge-tag">Nearest 100</span>
    </div>

    
    <div class="digits-row">
      
      <div class="digit-slot">
        <div class="carry-bubble" id="carryThous">+1 Carry</div>
        <div class="place-label">Thous</div>
        <div class="digit-box" id="dThous">6</div>
      </div>

      
      <div class="digit-slot">
        <div class="carry-bubble" id="carryHund">+1</div>
        <div class="place-label">Hund</div>
        <div class="digit-box" id="dHund">9</div>
      </div>

      
      <div class="digit-slot">
        <div class="place-label">Tens</div>
        <div class="digit-box" id="dTens">7</div>
      </div>

      
      <div class="digit-slot">
        <div class="place-label">Ones</div>
        <div class="digit-box" id="dOnes">1</div>
      </div>
    </div>

    
    <div class="info-card" id="infoCard">
      <div class="formula-row" id="formulaBox"></div>
      <div class="step-desc" id="descBox"></div>
    </div>

    
    <div class="controls">
      <button class="play-btn" id="playToggle" title="Auto play / pause">⏸</button>
      <button class="step-btn active" id="btn0">1. Identify</button>
      <button class="step-btn" id="btn1">2. Rollover</button>
      <button class="step-btn" id="btn2">3. Result</button>
    </div>
  </div>

  <script>
    const dThous = document.getElementById('dThous');
    const dHund = document.getElementById('dHund');
    const dTens = document.getElementById('dTens');
    const dOnes = document.getElementById('dOnes');
    const carryThous = document.getElementById('carryThous');
    const carryHund = document.getElementById('carryHund');
    const formulaBox = document.getElementById('formulaBox');
    const descBox = document.getElementById('descBox');
    const playToggle = document.getElementById('playToggle');

    const stepBtns = [
      document.getElementById('btn0'),
      document.getElementById('btn1'),
      document.getElementById('btn2')
    ];

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

    function renderStep(idx) {
      currentStep = idx;

      // Reset base class styling
      [dThous, dHund, dTens, dOnes].forEach(el => {
        el.className = 'digit-box';
      });
      carryThous.classList.remove('active');
      carryHund.classList.remove('active');

      stepBtns.forEach((btn, i) => {
        btn.classList.toggle('active', i === idx);
      });

      if (idx === 0) {
        // Step 1: Identify hundreds digit (9) and look at tens digit (7)
        dThous.textContent = '6';
        dHund.textContent = '9';
        dTens.textContent = '7';
        dOnes.textContent = '1';

        dHund.classList.add('highlight-target');
        dTens.classList.add('highlight-look');

        formulaBox.innerHTML = '<span class="pill pill-blue">Target: 9</span><span class="pill pill-amber">Look at: 7 ≥ 5</span>';
        descBox.textContent = 'Look at the tens digit (7). Since 7 ≥ 5, we must round up and add +1 to the hundreds place.';
      } 
      else if (idx === 1) {
        // Step 2: Since 7 >= 5, 9 + 1 = 10 (Rollover)
        dThous.textContent = '6';
        dHund.textContent = '9';
        dTens.textContent = '7';
        dOnes.textContent = '1';

        dHund.classList.add('highlight-rollover');
        carryHund.classList.add('active');

        formulaBox.innerHTML = '<span class="pill pill-purple">9 + 1 = 10</span>';
        descBox.textContent = 'Rollover! 9 becomes 10, so 0 stays in the hundreds place and +1 carries over to the thousands place.';
      } 
      else if (idx === 2) {
        // Step 3: Carry 1 to thousands (6 + 1 = 7), hundreds becomes 0, rest zeroed -> 7,000
        dThous.textContent = '7';
        dHund.textContent = '0';
        dTens.textContent = '0';
        dOnes.textContent = '0';

        dThous.classList.add('highlight-final');
        dHund.classList.add('highlight-final');
        dTens.classList.add('zeroed');
        dOnes.classList.add('zeroed');
        carryThous.classList.add('active');

        formulaBox.innerHTML = '<span class="pill pill-purple">6 + 1 = 7</span><span class="pill pill-green">Final: 7,000</span>';
        descBox.textContent = 'Thousands digit becomes 7 (6 + 1 = 7). Lower digits become 0. Rounded result is 7,000.';
      }
    }

    function startAutoPlay() {
      stopAutoPlay();
      isPlaying = true;
      playToggle.textContent = '⏸';
      autoInterval = setInterval(() => {
        const next = (currentStep + 1) % 3;
        renderStep(next);
      }, 3200);
    }

    function stopAutoPlay() {
      isPlaying = false;
      playToggle.textContent = '▶';
      if (autoInterval) {
        clearInterval(autoInterval);
        autoInterval = null;
      }
    }

    // Step button clicks
    stepBtns.forEach((btn, i) => {
      btn.addEventListener('click', () => {
        stopAutoPlay();
        renderStep(i);
      });
    });

    // Play/pause button click
    playToggle.addEventListener('click', () => {
      if (isPlaying) {
        stopAutoPlay();
      } else {
        startAutoPlay();
      }
    });

    // Initial render
    renderStep(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">
  <title>Rounding to the Nearest Ten</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      user-select: none;
      -webkit-user-select: none;
    }
    body {
      background: #f8f9fa;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      padding: 12px 16px 16px;
      overflow-x: hidden;
    }

    .header-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      max-width: 540px;
      margin-bottom: 4px;
    }
    .badge {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      padding: 4px 10px;
      border-radius: 20px;
      background: #e0e7ff;
      color: #3730a3;
    }
    .selector-row {
      display: flex;
      align-items: center;
      gap: 6px;
      flex-wrap: wrap;
      justify-content: center;
      margin: 6px 0;
    }
    .num-btn {
      background: #ffffff;
      border: 1.5px solid #cbd5e1;
      color: #475569;
      font-weight: 700;
      font-size: 14px;
      padding: 5px 9px;
      border-radius: 8px;
      cursor: pointer;
      transition: all 0.2s ease;
      min-width: 34px;
      text-align: center;
    }
    .num-btn:hover {
      border-color: #7c3aed;
      color: #7c3aed;
    }
    .num-btn.active {
      background: #1e2945;
      border-color: #1e2945;
      color: #ffffff;
      box-shadow: 0 2px 8px rgba(30, 41, 69, 0.25);
    }
    .num-btn.midpoint {
      border-color: #c4b5fd;
      color: #6d28d9;
    }
    .num-btn.midpoint.active {
      background: #7c3aed;
      border-color: #7c3aed;
      color: #ffffff;
    }

    .svg-container {
      width: 100%;
      max-width: 580px;
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }

    .caption-card {
      width: 100%;
      max-width: 540px;
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 16px;
      text-align: center;
      font-size: 15px;
      font-weight: 600;
      color: #1e2945;
      box-shadow: 0 2px 6px rgba(0, 0, 0, 0.04);
      margin-top: 4px;
      min-height: 48px;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    .caption-highlight {
      color: #0284c7;
      font-weight: 700;
    }
    .caption-round {
      color: #16a34a;
      font-weight: 800;
    }

    /* Glow animation for active marker */
    @keyframes pulseGlow {
      0% { r: 9px; opacity: 0.7; }
      50% { r: 15px; opacity: 0.2; }
      100% { r: 9px; opacity: 0.7; }
    }
    .glow-ring {
      animation: pulseGlow 2s infinite ease-in-out;
      transform-origin: center;
    }

    /* Animated dash for arcs */
    @keyframes drawDash {
      to { stroke-dashoffset: 0; }
    }
    .arc-solid {
      stroke-dasharray: 400;
      stroke-dashoffset: 400;
      animation: drawDash 0.8s ease-out forwards;
    }
  </style>
</head>
<body>

  <div class="header-bar">
    <span class="badge">Rounding to Nearest 10</span>
  </div>

  <div class="selector-row" id="numSelector">
    
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 540 220" id="numberLineSvg" xmlns="http://www.w3.org/2000/svg">
      <defs>
        
        <marker id="arrow-blue" markerWidth="8" markerHeight="8" refX="5" refY="3.5" orient="auto">
          <polygon points="0 0, 7 3.5, 0 7" fill="#0284c7"/>
        </marker>
        <marker id="arrow-purple" markerWidth="8" markerHeight="8" refX="5" refY="3.5" orient="auto">
          <polygon points="0 0, 7 3.5, 0 7" fill="#7c3aed"/>
        </marker>
        <marker id="arrow-gray" markerWidth="8" markerHeight="8" refX="5" refY="3.5" orient="auto">
          <polygon points="0 0, 7 3.5, 0 7" fill="#64748b"/>
        </marker>
        <marker id="arrow-green" markerWidth="8" markerHeight="8" refX="5" refY="3.5" orient="auto">
          <polygon points="0 0, 7 3.5, 0 7" fill="#16a34a"/>
        </marker>

        
        <filter id="shadow" x="-20%" y="-20%" width="140%" height="140%">
          <feDropShadow dx="0" dy="2" stdDeviation="3" flood-color="#000" flood-opacity="0.12"/>
        </filter>
      </defs>

      
      <path id="arcTo30" fill="none" stroke="#64748b" stroke-width="2.5" stroke-dasharray="6,4" marker-end="url(#arrow-gray)"/>
      <g id="labelGroup30">
        <rect id="labelBg30" rx="6" fill="#ffffff" stroke="#cbd5e1" stroke-width="1.5" filter="url(#shadow)"/>
        <text id="labelText30" font-size="13" font-weight="700" fill="#475569" text-anchor="middle" dominant-baseline="central"></text>
      </g>

      
      <path id="arcTo40" fill="none" stroke="#0284c7" stroke-width="3" marker-end="url(#arrow-blue)"/>
      <g id="labelGroup40">
        <rect id="labelBg40" rx="6" fill="#ffffff" stroke="#38bdf8" stroke-width="1.5" filter="url(#shadow)"/>
        <text id="labelText40" font-size="13" font-weight="700" fill="#0284c7" text-anchor="middle" dominant-baseline="central"></text>
      </g>

      
      <line x1="270" y1="52" x2="270" y2="185" stroke="#7c3aed" stroke-width="2" stroke-dasharray="5,4" opacity="0.85"/>
      <g transform="translate(270, 42)">
        <rect x="-42" y="-12" width="84" height="22" rx="11" fill="#f5f3ff" stroke="#7c3aed" stroke-width="1.5"/>
        <text font-size="11" font-weight="700" fill="#7c3aed" text-anchor="middle" dominant-baseline="central">MIDPOINT 35</text>
      </g>

      
      <line x1="45" y1="160" x2="495" y2="160" stroke="#94a3b8" stroke-width="4" stroke-linecap="round"/>

      
      <g id="ticksGroup"></g>

      
      <g id="activeMarkerGroup">
        <circle id="markerGlow" cx="0" cy="160" r="14" fill="#0284c7" class="glow-ring"/>
        <circle id="markerDot" cx="0" cy="160" r="8.5" fill="#0284c7" stroke="#ffffff" stroke-width="3"/>
        <g id="markerTag" transform="translate(0, 198)">
          <polygon points="-6,-6 0,-12 6,-6" fill="#1e2945"/>
          <rect x="-18" y="-6" width="36" height="24" rx="6" fill="#1e2945"/>
          <text id="markerTagText" font-size="14" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central" y="6">37</text>
        </g>
      </g>
    </svg>
  </div>

  <div class="caption-card" id="captionText">
    37 is closer to 40 than to 30, so 37 rounds up to 40.
  </div>

  <script>
    const X_START = 55;
    const X_END = 485;
    const TOTAL_STEPS = 10;
    const STEP_WIDTH = (X_END - X_START) / TOTAL_STEPS; // 43px per unit
    const LINE_Y = 160;

    let currentNum = 37;

    function getX(num) {
      return X_START + (num - 30) * STEP_WIDTH;
    }

    // Build Static Ticks
    const ticksGroup = document.getElementById('ticksGroup');
    for (let i = 0; i <= 10; i++) {
      const val = 30 + i;
      const x = getX(val);
      const isEndpoint = (i === 0 || i === 10);
      const isMid = (i === 5);

      // Tick line
      const tick = document.createElementNS('http://www.w3.org/2000/svg', 'line');
      tick.setAttribute('x1', x);
      tick.setAttribute('x2', x);
      tick.setAttribute('y1', isEndpoint ? LINE_Y - 14 : (isMid ? LINE_Y - 12 : LINE_Y - 7));
      tick.setAttribute('y2', isEndpoint ? LINE_Y + 14 : (isMid ? LINE_Y + 12 : LINE_Y + 7));
      tick.setAttribute('stroke', isEndpoint ? '#1e2945' : (isMid ? '#7c3aed' : '#94a3b8'));
      tick.setAttribute('stroke-width', isEndpoint ? '4' : (isMid ? '3' : '2'));
      ticksGroup.appendChild(tick);

      // Endpoint circle anchors
      if (isEndpoint) {
        const circle = document.createElementNS('http://www.w3.org/2000/svg', 'circle');
        circle.setAttribute('cx', x);
        circle.setAttribute('cy', LINE_Y);
        circle.setAttribute('r', '7');
        circle.setAttribute('fill', '#1e2945');
        ticksGroup.appendChild(circle);

        const lbl = document.createElementNS('http://www.w3.org/2000/svg', 'text');
        lbl.setAttribute('x', x);
        lbl.setAttribute('y', LINE_Y + 34);
        lbl.setAttribute('text-anchor', 'middle');
        lbl.setAttribute('font-size', '17');
        lbl.setAttribute('font-weight', '800');
        lbl.setAttribute('fill', '#1e2945');
        lbl.textContent = val;
        ticksGroup.appendChild(lbl);
      } else if (!isMid) {
        // Subtle numbers under ticks
        const lbl = document.createElementNS('http://www.w3.org/2000/svg', 'text');
        lbl.setAttribute('x', x);
        lbl.setAttribute('y', LINE_Y + 26);
        lbl.setAttribute('text-anchor', 'middle');
        lbl.setAttribute('font-size', '12');
        lbl.setAttribute('font-weight', '600');
        lbl.setAttribute('fill', '#94a3b8');
        lbl.textContent = val;
        ticksGroup.appendChild(lbl);
      }
    }

    // Build Selector Buttons
    const selector = document.getElementById('numSelector');
    for (let n = 31; n <= 39; n++) {
      const btn = document.createElement('button');
      btn.className = `num-btn ${n === 35 ? 'midpoint' : ''} ${n === 37 ? 'active' : ''}`;
      btn.textContent = n;
      btn.setAttribute('aria-label', `Select number ${n}`);
      btn.onclick = () => selectNumber(n);
      selector.appendChild(btn);
    }

    function selectNumber(num) {
      currentNum = num;
      // Update buttons
      document.querySelectorAll('.num-btn').forEach(btn => {
        btn.classList.toggle('active', parseInt(btn.textContent) === num);
      });
      renderDiagram(num);
    }

    function renderDiagram(num) {
      const xTarget = getX(num);
      const x30 = getX(30);
      const x40 = getX(40);

      const dist30 = num - 30;
      const dist40 = 40 - num;

      // Update Marker position
      const markerGroup = document.getElementById('activeMarkerGroup');
      const markerGlow = document.getElementById('markerGlow');
      const markerDot = document.getElementById('markerDot');
      const markerTag = document.getElementById('markerTag');
      const markerTagText = document.getElementById('markerTagText');

      markerGlow.setAttribute('cx', xTarget);
      markerDot.setAttribute('cx', xTarget);
      markerTag.setAttribute('transform', `translate(${xTarget}, 198)`);
      markerTagText.textContent = num;

      const markerColor = (num > 35) ? '#0284c7' : (num < 35 ? '#d97706' : '#7c3aed');
      markerGlow.setAttribute('fill', markerColor);
      markerDot.setAttribute('fill', markerColor);

      // Arc to 30 (Curves above)
      // Height proportional to distance
      const arc30Height = Math.max(28, dist30 * 9);
      const path30 = document.getElementById('arcTo30');
      const labelGroup30 = document.getElementById('labelGroup30');
      const labelBg30 = document.getElementById('labelBg30');
      const labelText30 = document.getElementById('labelText30');

      const midX30 = (xTarget + x30) / 2;
      const peakY30 = LINE_Y - 18 - arc30Height;

      // Path from xTarget back to x30
      path30.setAttribute('d', `M ${xTarget - 4} ${LINE_Y - 14} Q ${midX30} ${peakY30} ${x30 + 6} ${LINE_Y - 14}`);
      labelText30.textContent = `Distance = ${dist30}`;
      const textW30 = dist30 >= 10 ? 84 : 80;
      labelBg30.setAttribute('x', midX30 - textW30 / 2);
      labelBg30.setAttribute('y', peakY30 - 18);
      labelBg30.setAttribute('width', textW30);
      labelBg30.setAttribute('height', 24);
      labelText30.setAttribute('x', midX30);
      labelText30.setAttribute('y', peakY30 - 6);

      // Arc to 40
      const arc40Height = Math.max(28, dist40 * 9);
      const path40 = document.getElementById('arcTo40');
      const labelGroup40 = document.getElementById('labelGroup40');
      const labelBg40 = document.getElementById('labelBg40');
      const labelText40 = document.getElementById('labelText40');

      const midX40 = (xTarget + x40) / 2;
      const peakY40 = LINE_Y - 18 - arc40Height;

      // Path from xTarget forward to x40
      path40.setAttribute('d', `M ${xTarget + 4} ${LINE_Y - 14} Q ${midX40} ${peakY40} ${x40 - 6} ${LINE_Y - 14}`);
      labelText40.textContent = `Distance = ${dist40}`;
      const textW40 = dist40 >= 10 ? 84 : 80;
      labelBg40.setAttribute('x', midX40 - textW40 / 2);
      labelBg40.setAttribute('y', peakY40 - 18);
      labelBg40.setAttribute('width', textW40);
      labelBg40.setAttribute('height', 24);
      labelText40.setAttribute('x', midX40);
      labelText40.setAttribute('y', peakY40 - 6);

      // Styling based on which is closer
      if (num === 37) {
        // Target requested styling: Solid blue arc to 40, dotted longer arc to 30
        path40.setAttribute('stroke', '#0284c7');
        path40.setAttribute('stroke-width', '3.5');
        path40.setAttribute('stroke-dasharray', 'none');
        path40.setAttribute('marker-end', 'url(#arrow-blue)');
        labelBg40.setAttribute('stroke', '#0284c7');
        labelBg40.setAttribute('fill', '#f0f9ff');
        labelText40.setAttribute('fill', '#0284c7');

        path30.setAttribute('stroke', '#94a3b8');
        path30.setAttribute('stroke-width', '2');
        path30.setAttribute('stroke-dasharray', '5,4');
        path30.setAttribute('marker-end', 'url(#arrow-gray)');
        labelBg30.setAttribute('stroke', '#cbd5e1');
        labelBg30.setAttribute('fill', '#ffffff');
        labelText30.setAttribute('fill', '#64748b');
      } else if (dist40 < dist30) {
        // Closer to 40 (Rounds up)
        path40.setAttribute('stroke', '#16a34a');
        path40.setAttribute('stroke-width', '3.5');
        path40.setAttribute('stroke-dasharray', 'none');
        path40.setAttribute('marker-end', 'url(#arrow-green)');
        labelBg40.setAttribute('stroke', '#16a34a');
        labelBg40.setAttribute('fill', '#f0fdf4');
        labelText40.setAttribute('fill', '#16a34a');

        path30.setAttribute('stroke', '#94a3b8');
        path30.setAttribute('stroke-width', '2');
        path30.setAttribute('stroke-dasharray', '5,4');
        path30.setAttribute('marker-end', 'url(#arrow-gray)');
        labelBg30.setAttribute('stroke', '#cbd5e1');
        labelBg30.setAttribute('fill', '#ffffff');
        labelText30.setAttribute('fill', '#64748b');
      } else if (dist30 < dist40) {
        // Closer to 30 (Rounds down)
        path30.setAttribute('stroke', '#16a34a');
        path30.setAttribute('stroke-width', '3.5');
        path30.setAttribute('stroke-dasharray', 'none');
        path30.setAttribute('marker-end', 'url(#arrow-green)');
        labelBg30.setAttribute('stroke', '#16a34a');
        labelBg30.setAttribute('fill', '#f0fdf4');
        labelText30.setAttribute('fill', '#16a34a');

        path40.setAttribute('stroke', '#94a3b8');
        path40.setAttribute('stroke-width', '2');
        path40.setAttribute('stroke-dasharray', '5,4');
        path40.setAttribute('marker-end', 'url(#arrow-gray)');
        labelBg40.setAttribute('stroke', '#cbd5e1');
        labelBg40.setAttribute('fill', '#ffffff');
        labelText40.setAttribute('fill', '#64748b');
      } else {
        // Exactly at midpoint 35
        path30.setAttribute('stroke', '#7c3aed');
        path30.setAttribute('stroke-width', '2.5');
        path30.setAttribute('stroke-dasharray', 'none');
        path30.setAttribute('marker-end', 'url(#arrow-purple)');
        labelBg30.setAttribute('stroke', '#7c3aed');
        labelBg30.setAttribute('fill', '#f5f3ff');
        labelText30.setAttribute('fill', '#7c3aed');

        path40.setAttribute('stroke', '#7c3aed');
        path40.setAttribute('stroke-width', '3');
        path40.setAttribute('stroke-dasharray', 'none');
        path40.setAttribute('marker-end', 'url(#arrow-purple)');
        labelBg40.setAttribute('stroke', '#7c3aed');
        labelBg40.setAttribute('fill', '#f5f3ff');
        labelText40.setAttribute('fill', '#7c3aed');
      }

      // Update bottom caption
      const caption = document.getElementById('captionText');
      if (num === 37) {
        caption.innerHTML = `<span><strong>37</strong> is closer to <strong>40</strong> than to <strong>30</strong>, so <strong>37</strong> rounds up to <span class="caption-round">40</span>.</span>`;
      } else if (dist40 < dist30) {
        caption.innerHTML = `<span><strong>${num}</strong> is closer to <strong>40</strong> (distance ${dist40}) than <strong>30</strong> (${dist30}), so it rounds up to <span class="caption-round">40</span>.</span>`;
      } else if (dist30 < dist40) {
        caption.innerHTML = `<span><strong>${num}</strong> is closer to <strong>30</strong> (distance ${dist30}) than <strong>40</strong> (${dist40}), so it rounds down to <span class="caption-round">30</span>.</span>`;
      } else {
        caption.innerHTML = `<span><strong>35</strong> is right in the middle! The rule says midpoints round up to <span class="caption-round">40</span>.</span>`;
      }
    }

    // Initial load
    renderDiagram(37);
  </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;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      padding: 12px;
      user-select: none;
    }

    .stepper-nav {
      display: flex;
      gap: 8px;
      margin-bottom: 16px;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 20px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
      transition: all 0.25s ease;
    }

    .step-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.25);
    }

    .main-board {
      width: 100%;
      max-width: 440px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
    }

    .digits-row {
      display: flex;
      gap: 8px;
      width: 100%;
      justify-content: center;
    }

    .digit-col {
      display: flex;
      flex-direction: column;
      align-items: center;
      flex: 1;
      max-width: 82px;
    }

    .place-label {
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      margin-bottom: 6px;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .digit-box {
      width: 100%;
      height: 72px;
      border-radius: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      position: relative;
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      transition: all 0.3s ease;
    }

    .digit-num {
      font-size: 32px;
      font-weight: 700;
      line-height: 1;
    }

    .role-badge {
      position: absolute;
      bottom: -10px;
      font-size: 10px;
      font-weight: 700;
      padding: 2px 6px;
      border-radius: 6px;
      display: flex;
      align-items: center;
      gap: 2px;
      white-space: nowrap;
    }

    /* Column Styles */
    .box-gray {
      color: #94a3b8;
      border-color: #e2e8f0;
      background: #f8fafc;
    }

    .box-target {
      color: #0369a1;
      background: #f0f9ff;
      border-color: #0284c7;
      box-shadow: 0 4px 12px rgba(2, 132, 199, 0.15);
    }
    .badge-target {
      background: #0284c7;
      color: #ffffff;
    }

    .box-look {
      color: #b45309;
      background: #fffbeb;
      border-color: #f59e0b;
      box-shadow: 0 4px 12px rgba(245, 158, 11, 0.15);
    }
    .badge-look {
      background: #f59e0b;
      color: #ffffff;
    }

    /* Transformation & Arrow Area */
    .action-zone {
      width: 100%;
      height: 48px;
      position: relative;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .svg-canvas {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
    }

    .rule-pill {
      background: #eff6ff;
      border: 1px solid #bfdbfe;
      color: #1d4ed8;
      font-size: 13px;
      font-weight: 700;
      padding: 5px 12px;
      border-radius: 20px;
      z-index: 2;
      opacity: 0;
      transform: translateY(4px);
      transition: all 0.3s ease;
    }
    .rule-pill.visible {
      opacity: 1;
      transform: translateY(0);
    }

    /* Result Row */
    .result-row {
      display: flex;
      gap: 8px;
      width: 100%;
      justify-content: center;
      opacity: 0.2;
      transform: translateY(4px);
      transition: all 0.3s ease;
    }
    .result-row.active {
      opacity: 1;
      transform: translateY(0);
    }

    .res-box {
      width: 100%;
      height: 64px;
      border-radius: 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 30px;
      font-weight: 700;
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      color: #64748b;
    }

    .res-bump {
      background: #f0f9ff;
      border-color: #0284c7;
      color: #0284c7;
    }

    .res-zero {
      background: #f0fdf4;
      border-color: #16a34a;
      color: #16a34a;
    }
  </style>
</head>
<body>

  <div class="stepper-nav">
    <button class="step-btn active" id="btn1" onclick="setStep(1)">1. Find Place</button>
    <button class="step-btn" id="btn2" onclick="setStep(2)">2. Check Right</button>
    <button class="step-btn" id="btn3" onclick="setStep(3)">3. Round</button>
  </div>

  <div class="main-board">
    
    <div class="digits-row">
      
      <div class="digit-col">
        <span class="place-label">Th</span>
        <div class="digit-box box-gray">
          <span class="digit-num">3</span>
        </div>
      </div>
      
      <div class="digit-col">
        <span class="place-label">H</span>
        <div class="digit-box box-gray">
          <span class="digit-num">4</span>
        </div>
      </div>
      
      <div class="digit-col">
        <span class="place-label">Tens</span>
        <div class="digit-box box-target">
          <span class="digit-num">2</span>
          <span class="role-badge badge-target">🎯 Target</span>
        </div>
      </div>
      
      <div class="digit-col">
        <span class="place-label">Ones</span>
        <div class="digit-box box-look">
          <span class="digit-num">8</span>
          <span class="role-badge badge-look">👁️ Look</span>
        </div>
      </div>
    </div>

    
    <div class="action-zone">
      <svg class="svg-canvas" id="arrowSvg" viewBox="0 0 440 48">
        <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="#2563eb"/>
          </marker>
        </defs>
        
        <path id="curvePath" d="M 370 12 C 340 38, 290 38, 255 16" fill="none" stroke="#2563eb" stroke-width="2.5" stroke-dasharray="4 4" marker-end="url(#arrow)" opacity="0"/>
      </svg>
      <div class="rule-pill" id="rulePill">8 ≥ 5 → Add 1 to Tens</div>
    </div>

    
    <div class="result-row" id="resultRow">
      <div class="digit-col">
        <div class="res-box">3</div>
      </div>
      <div class="digit-col">
        <div class="res-box">4</div>
      </div>
      <div class="digit-col">
        <div class="res-box res-bump" id="resTens">3</div>
      </div>
      <div class="digit-col">
        <div class="res-box res-zero" id="resOnes">0</div>
      </div>
    </div>
  </div>

  <script>
    let currentStep = 1;
    let autoTimer = null;

    function setStep(step) {
      currentStep = step;
      
      // Update Button UI
      document.querySelectorAll('.step-btn').forEach((btn, idx) => {
        btn.classList.toggle('active', idx + 1 === step);
      });

      const curvePath = document.getElementById('curvePath');
      const rulePill = document.getElementById('rulePill');
      const resultRow = document.getElementById('resultRow');

      if (step === 1) {
        curvePath.setAttribute('opacity', '0');
        rulePill.classList.remove('visible');
        resultRow.classList.remove('active');
      } else if (step === 2) {
        curvePath.setAttribute('opacity', '1');
        rulePill.classList.add('visible');
        resultRow.classList.remove('active');
      } else if (step === 3) {
        curvePath.setAttribute('opacity', '1');
        rulePill.classList.add('visible');
        resultRow.classList.add('active');
      }
    }

    function autoCycle() {
      let next = currentStep + 1;
      if (next > 3) next = 1;
      setStep(next);
    }

    // Pedagogical cycle: advance every 3.5 seconds
    autoTimer = setInterval(autoCycle, 3500);

    // Pause on manual tap
    document.querySelectorAll('.step-btn').forEach(btn => {
      btn.addEventListener('click', () => {
        clearInterval(autoTimer);
        autoTimer = setInterval(autoCycle, 4500);
      });
    });
  </script>
</body>
</html>

OGM.6.NBT.3

Aligned learning resources

Related diagrams