<!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: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 16px 12px;
      user-select: none;
    }

    .stepper-nav {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      max-width: 440px;
    }

    .step-btn {
      flex: 1;
      padding: 8px 10px;
      font-size: 14px;
      font-weight: 600;
      border: 1px solid #e2e8f0;
      background: #f8fafc;
      color: #64748b;
      border-radius: 8px;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: all 0.2s ease;
    }

    .step-btn.active {
      background: #22b7ff;
      border-color: #22b7ff;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(34, 183, 255, 0.3);
    }

    .play-btn {
      padding: 8px 12px;
      font-size: 14px;
      border: 1px solid #e2e8f0;
      background: #f8fafc;
      color: #1e2945;
      border-radius: 8px;
      cursor: pointer;
      font-weight: 600;
    }

    .stage-container {
      position: relative;
      width: 100%;
      max-width: 480px;
      height: 220px;
      display: flex;
      align-items: center;
      justify-content: center;
      margin: auto 0;
    }

    .step-panel {
      position: absolute;
      inset: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease, transform 0.3s ease;
      transform: translateY(6px);
    }

    .step-panel.active {
      opacity: 1;
      pointer-events: auto;
      transform: translateY(0);
    }

    /* Math typography */
    .math-row {
      display: inline-flex;
      align-items: center;
      font-size: 26px;
      font-weight: 600;
      color: #1e2945;
      line-height: 1;
    }

    .fraction {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      vertical-align: middle;
      padding: 0 4px;
      margin: 0 4px;
    }

    .numerator {
      padding-bottom: 5px;
      border-bottom: 2.5px solid #1e2945;
      text-align: center;
      width: 100%;
    }

    .denominator {
      padding-top: 5px;
      text-align: center;
      width: 100%;
    }

    .op {
      margin: 0 8px;
      color: #64748b;
      font-weight: 500;
    }

    .unit {
      color: #0284c7;
      margin-left: 2px;
      position: relative;
      display: inline-block;
    }

    /* Cancellation Slash */
    .cancel-unit {
      position: relative;
      display: inline-block;
      color: #0284c7;
    }

    .slash {
      position: absolute;
      top: 50%;
      left: -15%;
      width: 130%;
      height: 3px;
      background-color: #ef4444;
      transform: translateY(-50%) rotate(-35deg);
      border-radius: 2px;
      opacity: 0;
      transform-origin: center;
      transition: opacity 0.3s ease, transform 0.3s ease;
    }

    .step-panel.active .slash {
      opacity: 1;
    }

    /* Step 3 Highlight Box */
    .result-box {
      border: 2.5px solid #16a34a;
      background: #f0fdf4;
      border-radius: 12px;
      padding: 16px 24px;
      box-shadow: 0 4px 12px rgba(22, 163, 74, 0.12);
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }

    .check-badge {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      background: #16a34a;
      color: #ffffff;
      width: 28px;
      height: 28px;
      border-radius: 50%;
      font-size: 16px;
      font-weight: bold;
      margin-left: 8px;
    }

    .sub-label {
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
      letter-spacing: 0.5px;
      text-transform: uppercase;
      margin-top: 14px;
    }

    @media (max-width: 400px) {
      .math-row {
        font-size: 21px;
      }
      .result-box {
        padding: 12px 16px;
      }
      .step-btn {
        font-size: 13px;
        padding: 6px 8px;
      }
    }
  </style>
</head>
<body>

  
  <div class="stepper-nav">
    <button class="step-btn active" id="btn0" onclick="goToStep(0)">1. Set Up</button>
    <button class="step-btn" id="btn1" onclick="goToStep(1)">2. Cancel</button>
    <button class="step-btn" id="btn2" onclick="goToStep(2)">3. Simplify</button>
    <button class="play-btn" id="playBtn" onclick="togglePlay()">⏸</button>
  </div>

  
  <div class="stage-container">
    
    
    <div class="step-panel active" id="panel0">
      <div class="math-row">
        <span>48<span class="unit">in</span></span>
        <span class="op">×</span>
        <div class="fraction">
          <div class="numerator">1<span class="unit">ft</span></div>
          <div class="denominator">12<span class="unit">in</span></div>
        </div>
      </div>
      <div class="sub-label">Conversion Ratio</div>
    </div>

    
    <div class="step-panel" id="panel1">
      <div class="math-row">
        <span>48<span class="cancel-unit">in<span class="slash"></span></span></span>
        <span class="op">×</span>
        <div class="fraction">
          <div class="numerator">1<span class="unit">ft</span></div>
          <div class="denominator">12<span class="cancel-unit">in<span class="slash"></span></span></div>
        </div>
      </div>
      <div class="sub-label" style="color: #ef4444;">Matching Units Cancel</div>
    </div>

    
    <div class="step-panel" id="panel2">
      <div class="result-box">
        <div class="math-row">
          <div class="fraction" style="margin-right: 8px;">
            <div class="numerator">48 × 1<span class="unit">ft</span></div>
            <div class="denominator">12</div>
          </div>
          <span class="op">=</span>
          <span style="color: #16a34a; font-weight: 700; margin-left: 4px;">4<span class="unit" style="color: #16a34a;">ft</span></span>
          <span class="check-badge">✓</span>
        </div>
      </div>
      <div class="sub-label" style="color: #16a34a;">Simplified Answer</div>
    </div>

  </div>

  <script src="{{VENDOR_CDN}}/classace-diagram.js"></script>
  <script>
    let currentStep = 0;
    const totalSteps = 3;
    let autoInterval = null;
    let isPlaying = true;

    function updateView() {
      for (let i = 0; i < totalSteps; i++) {
        const btn = document.getElementById('btn' + i);
        const panel = document.getElementById('panel' + i);
        if (i === currentStep) {
          btn.classList.add('active');
          panel.classList.add('active');
        } else {
          btn.classList.remove('active');
          panel.classList.remove('active');
        }
      }
    }

    function goToStep(idx) {
      currentStep = idx;
      updateView();
    }

    function nextStep() {
      currentStep = (currentStep + 1) % totalSteps;
      updateView();
    }

    function startAutoPlay() {
      if (autoInterval) clearInterval(autoInterval);
      autoInterval = setInterval(nextStep, 3500);
      isPlaying = true;
      document.getElementById('playBtn').textContent = '⏸';
    }

    function pauseAutoPlay() {
      if (autoInterval) clearInterval(autoInterval);
      autoInterval = null;
      isPlaying = false;
      document.getElementById('playBtn').textContent = '▶';
    }

    function togglePlay() {
      if (isPlaying) {
        pauseAutoPlay();
      } else {
        nextStep();
        startAutoPlay();
      }
    }

    // Initialize auto stepper
    startAutoPlay();
  </script>
</body>
</html>

Understanding Unit Conversion Within Measurement Systems

<!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;
      padding: 12px 8px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      user-select: none;
    }

    .diagram-container {
      width: 100%;
      max-width: 600px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }

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

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

    .btn-step {
      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 ease, color 0.2s ease, box-shadow 0.2s ease;
    }

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

    .btn-step.active {
      background: #2563eb;
      border-color: #2563eb;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(37, 99, 235, 0.25);
    }

    .callout-badge {
      text-anchor: middle;
      font-weight: 700;
      font-size: 13px;
    }

    .segment-clickable {
      cursor: pointer;
      transition: opacity 0.25s ease;
    }
  </style>
</head>
<body>

<div class="diagram-container">
  <svg viewBox="0 0 580 300" id="rulerSvg">
    <defs>
      
      <linearGradient id="woodGrad" x1="0%" y1="0%" x2="0%" y2="100%">
        <stop offset="0%" stop-color="#e3be8e"/>
        <stop offset="50%" stop-color="#d4a366"/>
        <stop offset="100%" stop-color="#c59253"/>
      </linearGradient>

      
      <linearGradient id="blueGrad" x1="0%" y1="0%" x2="0%" y2="100%">
        <stop offset="0%" stop-color="#3b82f6"/>
        <stop offset="100%" stop-color="#1d4ed8"/>
      </linearGradient>

      
      <linearGradient id="orangeGrad" x1="0%" y1="0%" x2="0%" y2="100%">
        <stop offset="0%" stop-color="#f97316"/>
        <stop offset="100%" stop-color="#c2410c"/>
      </linearGradient>

      
      <filter id="glow" x="-10%" y="-10%" width="120%" height="120%">
        <feDropShadow dx="0" dy="2" stdDeviation="3" flood-color="#2563eb" flood-opacity="0.2"/>
      </filter>
    </defs>

    
    <g stroke="#94a3b8" stroke-dasharray="3 3" stroke-width="1.5">
      <line x1="50" y1="35" x2="50" y2="225" />
      <line x1="210" y1="75" x2="210" y2="225" />
      <line x1="370" y1="75" x2="370" y2="225" />
      <line x1="530" y1="35" x2="530" y2="225" />
    </g>

    
    <g id="yardTier">
      <rect x="50" y="35" width="480" height="38" rx="5" fill="url(#woodGrad)" stroke="#8a5a2b" stroke-width="1.5"/>
      <text x="290" y="59" fill="#452203" font-size="15" font-weight="700" text-anchor="middle" letter-spacing="0.5">1 YARD (yd)</text>
    </g>

    
    <g id="feetTier">
      
      <g class="segment-clickable" id="segFt1" onclick="setHighlight(0)">
        <rect id="ftBox1" x="50" y="90" width="160" height="42" fill="#eff6ff" stroke="#2563eb" stroke-width="2" rx="4"/>
        <text x="130" y="116" fill="#1d4ed8" font-size="15" font-weight="700" text-anchor="middle">1 ft</text>
      </g>
      
      <g class="segment-clickable" id="segFt2" onclick="setHighlight(1)">
        <rect id="ftBox2" x="210" y="90" width="160" height="42" fill="#eff6ff" stroke="#2563eb" stroke-width="2" rx="4"/>
        <text x="290" y="116" fill="#1d4ed8" font-size="15" font-weight="700" text-anchor="middle">2 ft</text>
      </g>
      
      <g class="segment-clickable" id="segFt3" onclick="setHighlight(2)">
        <rect id="ftBox3" x="370" y="90" width="160" height="42" fill="#eff6ff" stroke="#2563eb" stroke-width="2" rx="4"/>
        <text x="450" y="116" fill="#1d4ed8" font-size="15" font-weight="700" text-anchor="middle">3 ft</text>
      </g>
    </g>

    
    <g id="inchesTier">
      
      <rect x="50" y="150" width="480" height="48" rx="4" fill="#fff7ed" stroke="#ea580c" stroke-width="2"/>

      
      <g id="inchTicks" stroke="#ea580c" stroke-linecap="round"></g>

      
      <text x="210" y="186" fill="#c2410c" font-size="13" font-weight="800" text-anchor="middle">12 in</text>
      <text x="370" y="186" fill="#c2410c" font-size="13" font-weight="800" text-anchor="middle">24 in</text>
      <text x="530" y="186" fill="#c2410c" font-size="13" font-weight="800" text-anchor="end">36 in</text>
    </g>

    
    <g id="highlightOverlay" pointer-events="none">
      
      <rect id="hlBox" x="50" y="88" width="160" height="112" rx="6" fill="rgba(37,99,235,0.08)" stroke="#2563eb" stroke-width="2.5" stroke-dasharray="6 4" />
      
      
      <g id="hlCallout" transform="translate(130, 245)">
        <rect x="-56" y="-18" width="112" height="28" rx="14" fill="#1e2945" />
        <text x="0" y="1" fill="#ffffff" class="callout-badge" text-anchor="middle" dominant-baseline="middle">1 ft = 12 in</text>
        <path d="M -6 -18 L 0 -24 L 6 -18 Z" fill="#1e2945" />
      </g>
    </g>
  </svg>

  
  <div class="controls">
    <button class="btn-step active" onclick="setHighlight(0)">1st Foot (12 in)</button>
    <button class="btn-step" onclick="setHighlight(1)">2nd Foot (24 in)</button>
    <button class="btn-step" onclick="setHighlight(2)">3rd Foot (36 in)</button>
    <button class="btn-step" onclick="setHighlight('all')">Full Yard (3 ft = 36 in)</button>
  </div>
</div>

<script>
  // Generate 36 precise inch tick marks
  const tickGroup = document.getElementById('inchTicks');
  const startX = 50;
  const totalWidth = 480;
  const inchWidth = totalWidth / 36; // 13.333px per inch

  for (let i = 0; i <= 36; i++) {
    const x = startX + i * inchWidth;
    const isMajor = (i % 12 === 0);
    const isMid = (i % 6 === 0 && !isMajor);
    
    const tickHeight = isMajor ? 20 : (isMid ? 13 : 8);
    const strokeW = isMajor ? 2 : 1;
    const opacity = isMajor ? 1 : 0.65;

    const line = document.createElementNS('http://www.w3.org/2000/svg', 'line');
    line.setAttribute('x1', x);
    line.setAttribute('y1', 150);
    line.setAttribute('x2', x);
    line.setAttribute('y2', 150 + tickHeight);
    line.setAttribute('stroke-width', strokeW);
    line.setAttribute('opacity', opacity);
    tickGroup.appendChild(line);
  }

  // Interactive Highlighting
  const hlBox = document.getElementById('hlBox');
  const hlCallout = document.getElementById('hlCallout');
  const calloutText = hlCallout.querySelector('text');
  const calloutPath = hlCallout.querySelector('path');
  const buttons = document.querySelectorAll('.btn-step');

  const positions = [
    { x: 50, w: 160, centerX: 130, text: '1 ft = 12 in' },
    { x: 210, w: 160, centerX: 290, text: '1 ft = 12 in' },
    { x: 370, w: 160, centerX: 450, text: '1 ft = 12 in' },
    { x: 50, w: 480, centerX: 290, text: '1 yd = 3 ft = 36 in' }
  ];

  function setHighlight(index) {
    const idx = (index === 'all') ? 3 : index;
    const pos = positions[idx];

    // Update active button
    buttons.forEach((btn, i) => {
      btn.classList.toggle('active', i === idx);
    });

    // Update highlight rectangle
    hlBox.setAttribute('x', pos.x);
    hlBox.setAttribute('width', pos.w);

    // Update Callout
    hlCallout.setAttribute('transform', `translate(${pos.centerX}, 245)`);
    calloutText.textContent = pos.text;

    // Adjust callout bubble width for longer "1 yd = 3 ft = 36 in" text
    const rect = hlCallout.querySelector('rect');
    if (idx === 3) {
      rect.setAttribute('x', '-85');
      rect.setAttribute('width', '170');
    } else {
      rect.setAttribute('x', '-56');
      rect.setAttribute('width', '112');
    }

    // Foot segment tinting
    for (let f = 1; f <= 3; f++) {
      const box = document.getElementById(`ftBox${f}`);
      if (idx === 3 || idx === (f - 1)) {
        box.setAttribute('fill', '#dbeafe');
        box.setAttribute('stroke', '#2563eb');
      } else {
        box.setAttribute('fill', '#f8fafc');
        box.setAttribute('stroke', '#94a3b8');
      }
    }
  }

  // Initialize
  setHighlight(0);
</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;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      user-select: none;
    }
    .layout {
      width: 100%;
      max-width: 620px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    .top-controls {
      display: flex;
      justify-content: space-between;
      align-items: center;
      padding: 0 4px;
      flex-wrap: wrap;
      gap: 8px;
    }
    .badge {
      font-size: 13px;
      font-weight: 700;
      color: #0284c7;
      background: #e0f2fe;
      padding: 4px 10px;
      border-radius: 999px;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }
    .btn-group {
      display: flex;
      gap: 6px;
    }
    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 600;
      padding: 4px 8px;
      cursor: pointer;
      color: #475569;
      transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
    }
    .step-btn:hover {
      background: #e2e8f0;
    }
    .step-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
    }
    .main-grid {
      display: grid;
      grid-template-columns: 1.2fr 0.8fr;
      gap: 12px;
      align-items: center;
    }
    @media (max-width: 520px) {
      .main-grid {
        grid-template-columns: 1fr;
      }
    }
    .line-container {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 10px 6px;
      position: relative;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }
    .table-container {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 6px;
    }
    table {
      width: 100%;
      border-collapse: collapse;
      font-size: 13px;
      text-align: center;
    }
    th {
      padding: 6px 4px;
      color: #64748b;
      font-weight: 700;
      font-size: 12px;
      border-bottom: 2px solid #cbd5e1;
    }
    td {
      padding: 5px 4px;
      font-weight: 600;
      color: #334155;
      border-bottom: 1px solid #e2e8f0;
      transition: background 0.2s ease, color 0.2s ease;
    }
    tr:last-child td {
      border-bottom: none;
    }
    tr.active td {
      background: #e0f2fe;
      color: #0369a1;
      font-weight: 700;
    }
    tr.active td:first-child {
      border-top-left-radius: 6px;
      border-bottom-left-radius: 6px;
    }
    tr.active td:last-child {
      border-top-right-radius: 6px;
      border-bottom-right-radius: 6px;
    }
    .unit-ft { color: #2563eb; }
    .unit-in { color: #d97706; }
    .rate { color: #059669; font-weight: 700; }
  </style>
</head>
<body>

<div class="layout">
  <div class="top-controls">
    <div class="badge">× 12 Conversion Factor</div>
    <div class="btn-group" id="btnGroup"></div>
  </div>

  <div class="main-grid">
    
    <div class="line-container">
      <svg viewBox="0 0 360 200" id="numLineSvg">
        
        <defs>
          <marker id="arrow-blue" viewBox="0 0 6 6" refX="5" refY="3" markerWidth="4" markerHeight="4" orient="auto">
            <path d="M 0 0 L 6 3 L 0 6 z" fill="#2563eb"/>
          </marker>
          <marker id="arrow-amber" viewBox="0 0 6 6" refX="5" refY="3" markerWidth="4" markerHeight="4" orient="auto">
            <path d="M 0 0 L 6 3 L 0 6 z" fill="#d97706"/>
          </marker>
          <marker id="arrow-center" viewBox="0 0 6 6" refX="5" refY="3" markerWidth="5" markerHeight="5" orient="auto">
            <path d="M 0 0 L 6 3 L 0 6 z" fill="#0284c7"/>
          </marker>
        </defs>

        
        <path id="topCurve" d="M 125 40 Q 175 15 225 40" fill="none" stroke="#2563eb" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-blue)" />
        <text id="topCurveText" x="175" y="24" font-size="11" font-weight="700" fill="#2563eb" text-anchor="middle">× 3</text>

        
        <text x="65" y="60" font-size="11" font-weight="700" fill="#2563eb" text-anchor="end" dominant-baseline="middle">Feet (x)</text>
        <line x1="75" y1="60" x2="335" y2="60" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round" />

        
        <g id="centerArrowGroup" transform="translate(225, 65)">
          <line x1="0" y1="3" x2="0" y2="67" stroke="#0284c7" stroke-width="2" marker-end="url(#arrow-center)"/>
          <rect x="-38" y="22" width="76" height="22" rx="4" fill="#ffffff" stroke="#0284c7" stroke-width="1.5"/>
          <text x="0" y="37" font-size="11" font-weight="700" fill="#0284c7" text-anchor="middle">× 12</text>
        </g>

        
        <text x="65" y="140" font-size="11" font-weight="700" fill="#d97706" text-anchor="end" dominant-baseline="middle">Inches (y)</text>
        <line x1="75" y1="140" x2="335" y2="140" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round" />

        
        <path id="botCurve" d="M 125 160 Q 175 185 225 160" fill="none" stroke="#d97706" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-amber)" />
        <text id="botCurveText" x="175" y="184" font-size="11" font-weight="700" fill="#d97706" text-anchor="middle">× 3</text>

        
        
        <g class="tick-group" data-idx="0" transform="translate(75, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <text x="0" y="48" font-size="12" font-weight="700" fill="#1e2945" text-anchor="middle">0</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <text x="0" y="159" font-size="12" font-weight="700" fill="#1e2945" text-anchor="middle">0</text>
        </g>

        
        <g class="tick-group" data-idx="1" transform="translate(125, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <circle id="c-top-1" cx="0" cy="60" r="4" fill="#2563eb" opacity="0"/>
          <text x="0" y="48" font-size="12" font-weight="700" fill="#2563eb" text-anchor="middle">1</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <circle id="c-bot-1" cx="0" cy="140" r="4" fill="#d97706" opacity="0"/>
          <text x="0" y="159" font-size="12" font-weight="700" fill="#d97706" text-anchor="middle">12</text>
        </g>

        
        <g class="tick-group" data-idx="2" transform="translate(175, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <circle id="c-top-2" cx="0" cy="60" r="4" fill="#2563eb" opacity="0"/>
          <text x="0" y="48" font-size="12" font-weight="700" fill="#2563eb" text-anchor="middle">2</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <circle id="c-bot-2" cx="0" cy="140" r="4" fill="#d97706" opacity="0"/>
          <text x="0" y="159" font-size="12" font-weight="700" fill="#d97706" text-anchor="middle">24</text>
        </g>

        
        <g class="tick-group" data-idx="3" transform="translate(225, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <circle id="c-top-3" cx="0" cy="60" r="5" fill="#2563eb"/>
          <text x="0" y="48" font-size="12" font-weight="700" fill="#2563eb" text-anchor="middle">3</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <circle id="c-bot-3" cx="0" cy="140" r="5" fill="#d97706"/>
          <text x="0" y="159" font-size="12" font-weight="700" fill="#d97706" text-anchor="middle">36</text>
        </g>

        
        <g class="tick-group" data-idx="4" transform="translate(275, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <circle id="c-top-4" cx="0" cy="60" r="4" fill="#2563eb" opacity="0"/>
          <text x="0" y="48" font-size="12" font-weight="700" fill="#2563eb" text-anchor="middle">4</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <circle id="c-bot-4" cx="0" cy="140" r="4" fill="#d97706" opacity="0"/>
          <text x="0" y="159" font-size="12" font-weight="700" fill="#d97706" text-anchor="middle">48</text>
        </g>

        
        <g class="tick-group" data-idx="5" transform="translate(325, 0)">
          <line x1="0" y1="53" x2="0" y2="67" stroke="#64748b" stroke-width="2" />
          <circle id="c-top-5" cx="0" cy="60" r="4" fill="#2563eb" opacity="0"/>
          <text x="0" y="48" font-size="12" font-weight="700" fill="#2563eb" text-anchor="middle">5</text>
          <line x1="0" y1="133" x2="0" y2="147" stroke="#64748b" stroke-width="2" />
          <circle id="c-bot-5" cx="0" cy="140" r="4" fill="#d97706" opacity="0"/>
          <text x="0" y="159" font-size="12" font-weight="700" fill="#d97706" text-anchor="middle">60</text>
        </g>
      </svg>
    </div>

    
    <div class="table-container">
      <table>
        <thead>
          <tr>
            <th class="unit-ft">Feet (x)</th>
            <th class="unit-in">Inches (y)</th>
            <th class="rate">y / x</th>
          </tr>
        </thead>
        <tbody id="tableBody">
          
        </tbody>
      </table>
    </div>
  </div>
</div>

<script>
  const data = [
    { ft: 1, in: 12, ratio: "12 / 1 = 12", xPos: 125 },
    { ft: 2, in: 24, ratio: "24 / 2 = 12", xPos: 175 },
    { ft: 3, in: 36, ratio: "36 / 3 = 12", xPos: 225 },
    { ft: 4, in: 48, ratio: "48 / 4 = 12", xPos: 275 },
    { ft: 5, in: 60, ratio: "60 / 5 = 12", xPos: 325 }
  ];

  let activeIdx = 2; // Default to 3 ft
  const tbody = document.getElementById('tableBody');
  const btnGroup = document.getElementById('btnGroup');

  // Build UI
  data.forEach((d, idx) => {
    // Buttons
    const btn = document.createElement('button');
    btn.className = `step-btn ${idx === activeIdx ? 'active' : ''}`;
    btn.textContent = `${d.ft} ft`;
    btn.onclick = () => selectStep(idx);
    btnGroup.appendChild(btn);

    // Table rows
    const tr = document.createElement('tr');
    tr.id = `row-${idx}`;
    tr.className = idx === activeIdx ? 'active' : '';
    tr.style.cursor = 'pointer';
    tr.onclick = () => selectStep(idx);
    tr.innerHTML = `
      <td class="unit-ft">${d.ft}</td>
      <td class="unit-in">${d.in}</td>
      <td class="rate">${d.ratio}</td>
    `;
    tbody.appendChild(tr);
  });

  function selectStep(idx) {
    activeIdx = idx;
    const d = data[idx];

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

    // Update table rows
    data.forEach((_, i) => {
      const r = document.getElementById(`row-${i}`);
      if (r) r.classList.toggle('active', i === idx);
    });

    // Update SVG elements
    const centerArrow = document.getElementById('centerArrowGroup');
    centerArrow.setAttribute('transform', `translate(${d.xPos}, 65)`);

    // Update Top & Bottom Curves
    const topCurve = document.getElementById('topCurve');
    const botCurve = document.getElementById('botCurve');
    const topText = document.getElementById('topCurveText');
    const botText = document.getElementById('botCurveText');

    if (idx === 0) {
      // 1 ft: hide multiplier curve
      topCurve.style.display = 'none';
      botCurve.style.display = 'none';
      topText.style.display = 'none';
      botText.style.display = 'none';
    } else {
      topCurve.style.display = 'block';
      botCurve.style.display = 'block';
      topText.style.display = 'block';
      botText.style.display = 'block';

      const midX = (125 + d.xPos) / 2;
      topCurve.setAttribute('d', `M 125 40 Q ${midX} 15 ${d.xPos} 40`);
      botCurve.setAttribute('d', `M 125 160 Q ${midX} 185 ${d.xPos} 160`);

      topText.setAttribute('x', midX);
      botText.setAttribute('x', midX);
      topText.textContent = `× ${d.ft}`;
      botText.textContent = `× ${d.ft}`;
    }

    // Dots on ticks
    for (let i = 1; i <= 5; i++) {
      const topC = document.getElementById(`c-top-${i}`);
      const botC = document.getElementById(`c-bot-${i}`);
      if (i === d.ft) {
        topC.setAttribute('opacity', '1');
        botC.setAttribute('opacity', '1');
      } else if (i === 1 && idx > 0) {
        topC.setAttribute('opacity', '0.4');
        botC.setAttribute('opacity', '0.4');
      } else {
        topC.setAttribute('opacity', '0');
        botC.setAttribute('opacity', '0');
      }
    }
  }

  // Initial draw
  selectStep(2);
</script>

</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Cross-Multiplication</title>
  <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: 16px 12px;
      user-select: none;
    }

    /* Top step selector */
    .stepper-nav {
      display: flex;
      align-items: center;
      gap: 8px;
      width: 100%;
      max-width: 380px;
      justify-content: center;
      margin-bottom: 20px;
    }
    .step-btn {
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      padding: 8px 12px;
      border-radius: 20px;
      border: 1.5px solid #cbd5e1;
      background: #ffffff;
      color: #64748b;
      font-size: 14px;
      font-weight: 700;
      cursor: pointer;
      transition: background-color 0.2s ease, color 0.2s ease, border-color 0.2s ease;
    }
    .step-btn:hover {
      border-color: #94a3b8;
      color: #1e2945;
    }
    .step-btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }
    .play-btn {
      width: 36px;
      height: 36px;
      border-radius: 50%;
      border: 1.5px solid #cbd5e1;
      background: #ffffff;
      color: #1e2945;
      font-size: 14px;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      flex-shrink: 0;
      transition: background-color 0.2s ease, border-color 0.2s ease;
    }
    .play-btn:hover {
      border-color: #94a3b8;
      background: #f1f5f9;
    }

    /* Main presentation stage */
    .stage {
      position: relative;
      width: 100%;
      max-width: 380px;
      height: 220px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .step-card {
      position: absolute;
      inset: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      opacity: 0;
      visibility: hidden;
      pointer-events: none;
      transition: opacity 0.25s ease, visibility 0.25s ease;
      padding: 8px;
    }
    .step-card.active {
      opacity: 1;
      visibility: visible;
      pointer-events: auto;
    }

    .step-label {
      font-size: 13px;
      font-weight: 600;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      margin-bottom: 12px;
    }

    /* Math typography */
    .fraction {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      vertical-align: middle;
      font-size: 26px;
      font-weight: 700;
      line-height: 1.15;
    }
    .fraction .num {
      padding: 2px 10px;
      border-bottom: 2.5px solid #1e2945;
      text-align: center;
    }
    .fraction .den {
      padding: 2px 10px;
      text-align: center;
    }

    /* Highlight Colors */
    .blue { color: #2563eb; }
    .orange { color: #ea580c; }
    .unit {
      font-size: 14px;
      font-weight: 600;
      color: #64748b;
      margin-left: 2px;
    }

    /* Step 1: Cross multiply layout */
    .cross-container {
      position: relative;
      width: 260px;
      height: 130px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 10px;
    }
    .cross-svg {
      position: absolute;
      inset: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
    }
    .eq-sign {
      font-size: 28px;
      font-weight: 700;
      color: #64748b;
    }

    /* Step 2: Equations */
    .eq-step {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }
    .eq-row {
      font-size: 24px;
      font-weight: 700;
      display: flex;
      align-items: center;
      gap: 12px;
    }
    .arrow-down {
      font-size: 18px;
      color: #94a3b8;
      line-height: 1;
    }

    /* Step 3: Solve Box */
    .solve-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }
    .solve-row {
      display: flex;
      align-items: center;
      gap: 12px;
      font-size: 24px;
      font-weight: 700;
    }
    .final-pill {
      background: #dcfce7;
      border: 2px solid #22c55e;
      color: #15803d;
      padding: 6px 20px;
      border-radius: 20px;
      font-size: 22px;
      font-weight: 800;
      margin-top: 4px;
    }
    .div-hint {
      font-size: 13px;
      font-weight: 700;
      color: #64748b;
      background: #f1f5f9;
      padding: 4px 12px;
      border-radius: 12px;
    }

    @media (max-width: 360px) {
      .fraction { font-size: 22px; }
      .eq-row, .solve-row { font-size: 21px; }
      .final-pill { font-size: 20px; padding: 5px 16px; }
      .cross-container { width: 230px; }
    }
  </style>
</head>
<body>

  
  <div class="stepper-nav">
    <button class="step-btn active" id="btn-0" type="button">Step 1</button>
    <button class="step-btn" id="btn-1" type="button">Step 2</button>
    <button class="step-btn" id="btn-2" type="button">Step 3</button>
    <button class="play-btn" id="playBtn" type="button" aria-label="Pause animation" title="Play / Pause">⏸</button>
  </div>

  
  <div class="stage">

    
    <div class="step-card active" id="step-0">
      <div class="step-label">1. Cross-Multiply Diagonals</div>
      <div class="cross-container">
        <svg class="cross-svg" viewBox="0 0 260 130">
          <defs>
            <marker id="arrow-blue" markerWidth="7" markerHeight="7" refX="5" refY="3.5" orient="auto">
              <polygon points="0 0, 7 3.5, 0 7" fill="#2563eb" />
            </marker>
            <marker id="arrow-orange" markerWidth="7" markerHeight="7" refX="5" refY="3.5" orient="auto">
              <polygon points="0 0, 7 3.5, 0 7" fill="#ea580c" />
            </marker>
          </defs>
          
          <line x1="58" y1="36" x2="200" y2="94" stroke="#2563eb" stroke-width="2.5" stroke-dasharray="5,4" marker-end="url(#arrow-blue)" />
          
          <line x1="58" y1="94" x2="200" y2="36" stroke="#ea580c" stroke-width="2.5" stroke-dasharray="5,4" marker-end="url(#arrow-orange)" />
        </svg>

        
        <div class="fraction">
          <div class="num blue">1<span class="unit">ft</span></div>
          <div class="den orange">12<span class="unit">in</span></div>
        </div>

        <div class="eq-sign">=</div>

        
        <div class="fraction">
          <div class="num orange">x<span class="unit">ft</span></div>
          <div class="den blue">54<span class="unit">in</span></div>
        </div>
      </div>
    </div>

    
    <div class="step-card" id="step-1">
      <div class="step-label">2. Set Up Equation</div>
      <div class="eq-step">
        <div class="eq-row">
          <span class="blue">1 · 54</span>
          <span>=</span>
          <span class="orange">12 · x</span>
        </div>
        <div class="arrow-down">↓</div>
        <div class="eq-row">
          <span class="blue">54</span>
          <span>=</span>
          <span class="orange">12x</span>
        </div>
      </div>
    </div>

    
    <div class="step-card" id="step-2">
      <div class="step-label">3. Solve for x</div>
      <div class="solve-box">
        <div class="div-hint">Divide both sides by 12</div>
        <div class="solve-row">
          <span>x =</span>
          <div class="fraction">
            <span class="num blue" style="border-bottom-width: 2px;">54</span>
            <span class="den orange">12</span>
          </div>
        </div>
        <div class="final-pill">
          x = 4.5 ft
        </div>
      </div>
    </div>

  </div>

  <script>
    const cards = [
      document.getElementById('step-0'),
      document.getElementById('step-1'),
      document.getElementById('step-2')
    ];
    const btns = [
      document.getElementById('btn-0'),
      document.getElementById('btn-1'),
      document.getElementById('btn-2')
    ];
    const playBtn = document.getElementById('playBtn');

    let current = 0;
    let playing = true;
    let timer = null;

    function showStep(idx) {
      current = idx;
      cards.forEach((c, i) => {
        if (c) c.classList.toggle('active', i === idx);
      });
      btns.forEach((b, i) => {
        if (b) b.classList.toggle('active', i === idx);
      });
    }

    function nextStep() {
      showStep((current + 1) % 3);
    }

    function startTimer() {
      clearInterval(timer);
      timer = setInterval(nextStep, 3500);
      playing = true;
      playBtn.textContent = '⏸';
      playBtn.setAttribute('aria-label', 'Pause animation');
    }

    function stopTimer() {
      clearInterval(timer);
      playing = false;
      playBtn.textContent = '▶';
      playBtn.setAttribute('aria-label', 'Play animation');
    }

    btns.forEach((btn, i) => {
      btn.addEventListener('click', () => {
        showStep(i);
        stopTimer();
      });
    });

    playBtn.addEventListener('click', () => {
      if (playing) {
        stopTimer();
      } else {
        nextStep();
        startTimer();
      }
    });

    startTimer();
  </script>
</body>
</html>

Using Proportions for Unit Conversions

<!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: #f8f9fa;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      user-select: none;
    }

    /* Stepper Navigation */
    .controls {
      display: flex;
      align-items: center;
      gap: 6px;
      flex-wrap: wrap;
      justify-content: center;
      width: 100%;
      margin-bottom: 8px;
    }
    .btn-step {
      background: #ffffff;
      border: 1px solid #d1d5db;
      color: #1e2945;
      padding: 5px 10px;
      font-size: 13px;
      font-weight: 600;
      border-radius: 6px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
      transition: background 0.2s, color 0.2s, border-color 0.2s, box-shadow 0.2s;
    }
    .btn-step.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 4px rgba(2, 132, 199, 0.25);
    }
    .play-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      width: 28px;
      height: 28px;
      display: flex;
      align-items: center;
      justify-content: center;
      border-radius: 50%;
      cursor: pointer;
      font-size: 11px;
    }

    /* Content Area */
    .stage {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      align-items: center;
      flex: 1;
      justify-content: center;
    }

    /* Ratio Cards Row */
    .proportions-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      width: 100%;
      position: relative;
    }
    .ratio-card {
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 10px;
      padding: 10px 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      width: 110px;
      box-shadow: 0 1px 3px rgba(0,0,0,0.05);
      transition: transform 0.25s, border-color 0.25s, box-shadow 0.25s;
    }
    .card-label {
      font-size: 11px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      margin-bottom: 6px;
    }
    .ratio-card.known { border-top: 3px solid #0284c7; }
    .ratio-card.unknown { border-top: 3px solid #d97706; }

    .fraction {
      display: flex;
      flex-direction: column;
      align-items: center;
      font-weight: 700;
      font-size: 16px;
      line-height: 1.2;
    }
    .numerator, .denominator {
      padding: 2px 6px;
      border-radius: 4px;
      transition: background 0.3s, color 0.3s;
    }
    .fraction-line {
      width: 100%;
      min-width: 44px;
      height: 2px;
      background: #1e2945;
      margin: 2px 0;
    }
    .equals-sign {
      font-size: 22px;
      font-weight: 700;
      color: #64748b;
    }

    /* Cross Multi Highlights */
    .hl-diag1 { background: #dbeafe; color: #1d4ed8; }
    .hl-diag2 { background: #fef3c7; color: #b45309; }

    /* SVG Cross Overlay */
    .cross-svg {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
      opacity: 0;
      transition: opacity 0.3s;
    }
    .cross-svg.active {
      opacity: 1;
    }

    /* Work and Solution Box */
    .algebra-box {
      width: 100%;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 10px 14px;
      display: flex;
      flex-direction: column;
      gap: 6px;
      align-items: center;
      min-height: 80px;
      justify-content: center;
    }
    .equation-line {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 16px;
      font-weight: 700;
      color: #1e2945;
      opacity: 0.3;
      transition: opacity 0.3s, transform 0.3s;
    }
    .equation-line.active {
      opacity: 1;
      transform: scale(1.03);
    }
    .result-badge {
      background: #ecfdf5;
      border: 1.5px solid #10b981;
      color: #047857;
      padding: 2px 10px;
      border-radius: 20px;
      font-size: 16px;
      font-weight: 800;
    }

    /* Visual Model: Pitchers & Cups */
    .visual-model {
      width: 100%;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 10px 12px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      align-items: center;
    }
    .model-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      flex-wrap: wrap;
      width: 100%;
    }
    .pitcher-group {
      display: flex;
      flex-direction: column;
      align-items: center;
      background: #f0f9ff;
      border: 1px solid #bae6fd;
      border-radius: 6px;
      padding: 4px 6px;
      min-width: 54px;
    }
    .pitcher-icon {
      font-size: 20px;
      line-height: 1;
    }
    .pitcher-sub {
      font-size: 10px;
      font-weight: 700;
      color: #0369a1;
      margin-top: 2px;
    }

    .cup-grid {
      display: grid;
      grid-template-columns: repeat(7, auto);
      gap: 4px;
      justify-content: center;
      align-items: center;
    }
    .cup-item {
      width: 22px;
      height: 22px;
      background: #fef3c7;
      border: 1px solid #fde68a;
      border-radius: 4px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 12px;
    }
    .model-summary {
      font-size: 13px;
      font-weight: 700;
      color: #334155;
      display: flex;
      align-items: center;
      gap: 6px;
    }

    @media (max-width: 400px) {
      .ratio-card { width: 96px; padding: 8px 10px; }
      .fraction { font-size: 14px; }
      .equation-line { font-size: 14px; }
      .cup-grid { grid-template-columns: repeat(7, 20px); gap: 3px; }
      .cup-item { width: 20px; height: 20px; font-size: 11px; }
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="play-btn" id="playBtn" title="Auto play">▶</button>
    <button class="btn-step active" data-step="0">1. Setup</button>
    <button class="btn-step" data-step="1">2. Cross Multiply</button>
    <button class="btn-step" data-step="2">3. Solve (x)</button>
    <button class="btn-step" data-step="3">4. Visual Check</button>
  </div>

  
  <div class="stage">
    
    
    <div class="proportions-row" id="propRow">
      
      <svg class="cross-svg" id="crossSvg" viewBox="0 0 300 100" preserveAspectRatio="none">
        <line x1="85" y1="30" x2="215" y2="70" stroke="#f59e0b" stroke-width="2.5" stroke-dasharray="4" />
        <line x1="85" y1="70" x2="215" y2="30" stroke="#3b82f6" stroke-width="2.5" stroke-dasharray="4" />
      </svg>

      
      <div class="ratio-card known">
        <span class="card-label">Known</span>
        <div class="fraction">
          <span class="numerator" id="numKnown">1 qt</span>
          <div class="fraction-line"></div>
          <span class="denominator" id="denKnown">4 cups</span>
        </div>
      </div>

      <div class="equals-sign">=</div>

      
      <div class="ratio-card unknown">
        <span class="card-label">Target</span>
        <div class="fraction">
          <span class="numerator" id="numUnk">x qt</span>
          <div class="fraction-line"></div>
          <span class="denominator" id="denUnk">14 cups</span>
        </div>
      </div>
    </div>

    
    <div class="algebra-box">
      <div class="equation-line" id="eqLine1">
        <span style="color:#2563eb;">4</span> · <span style="color:#2563eb;">x</span>
        <span>=</span>
        <span style="color:#d97706;">1</span> · <span style="color:#d97706;">14</span>
      </div>
      <div class="equation-line" id="eqLine2">
        <span>4x = 14</span>
        <span style="color:#64748b; font-weight:400; font-size:14px;">→</span>
        <span>x = 14 ÷ 4</span>
      </div>
      <div class="equation-line" id="eqLine3">
        <span>Result:</span>
        <span class="result-badge">x = 3.5 quarts</span>
      </div>
    </div>

    
    <div class="visual-model">
      <div class="model-row">
        
        <div class="pitcher-group">
          <span class="pitcher-icon">🫖</span>
          <span class="pitcher-sub">1 qt</span>
        </div>
        <div class="pitcher-group">
          <span class="pitcher-icon">🫖</span>
          <span class="pitcher-sub">1 qt</span>
        </div>
        <div class="pitcher-group">
          <span class="pitcher-icon">🫖</span>
          <span class="pitcher-sub">1 qt</span>
        </div>
        <div class="pitcher-group" style="opacity: 0.8; border-style: dashed;">
          <span class="pitcher-icon">🫖</span>
          <span class="pitcher-sub">0.5 qt</span>
        </div>

        <div class="equals-sign" style="font-size: 18px;">=</div>

        
        <div class="cup-grid">
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
          <div class="cup-item" title="1 cup">🥛</div>
        </div>
      </div>
      <div class="model-summary">
        <span>3.5 Quarts</span>
        <span style="color:#94a3b8;">=</span>
        <span>14 Cups</span>
        <span style="font-weight:400; font-size:12px; color:#64748b;">(4 + 4 + 4 + 2)</span>
      </div>
    </div>

  </div>

  <script>
    const steps = [
      {
        hlDiag1: false, hlDiag2: false, cross: false,
        eq1: false, eq2: false, eq3: false
      },
      {
        hlDiag1: true, hlDiag2: true, cross: true,
        eq1: true, eq2: false, eq3: false
      },
      {
        hlDiag1: false, hlDiag2: false, cross: false,
        eq1: true, eq2: true, eq3: true
      },
      {
        hlDiag1: false, hlDiag2: false, cross: false,
        eq1: true, eq2: true, eq3: true
      }
    ];

    let currentStep = 0;
    let timer = null;

    const numKnown = document.getElementById('numKnown');
    const denKnown = document.getElementById('denKnown');
    const numUnk = document.getElementById('numUnk');
    const denUnk = document.getElementById('denUnk');
    const crossSvg = document.getElementById('crossSvg');

    const eqLine1 = document.getElementById('eqLine1');
    const eqLine2 = document.getElementById('eqLine2');
    const eqLine3 = document.getElementById('eqLine3');

    const stepButtons = document.querySelectorAll('.btn-step');
    const playBtn = document.getElementById('playBtn');

    function render(stepIdx) {
      currentStep = stepIdx;
      
      // Update buttons
      stepButtons.forEach((btn, idx) => {
        btn.classList.toggle('active', idx === stepIdx);
      });

      // Highlights
      if (stepIdx === 1) {
        denKnown.classList.add('hl-diag1');
        numUnk.classList.add('hl-diag1');
        numKnown.classList.add('hl-diag2');
        denUnk.classList.add('hl-diag2');
        crossSvg.classList.add('active');
      } else {
        denKnown.classList.remove('hl-diag1');
        numUnk.classList.remove('hl-diag1');
        numKnown.classList.remove('hl-diag2');
        denUnk.classList.remove('hl-diag2');
        crossSvg.classList.remove('active');
      }

      // Equation visibility
      eqLine1.classList.toggle('active', stepIdx >= 1);
      eqLine2.classList.toggle('active', stepIdx >= 2);
      eqLine3.classList.toggle('active', stepIdx >= 2);
    }

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

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

    function startAutoPlay() {
      playBtn.textContent = '⏸';
      timer = setInterval(nextStep, 3500);
    }

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

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

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

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e293b;
      background: transparent;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      box-sizing: border-box;
      user-select: none;
    }

    /* Stepper Controls */
    .controls {
      display: flex;
      gap: 6px;
      width: 100%;
      max-width: 380px;
      margin-bottom: 8px;
    }
    .btn {
      flex: 1;
      border: 1px solid #cbd5e1;
      background: #f8fafc;
      color: #475569;
      padding: 7px 2px;
      font-size: clamp(11px, 3.2vw, 13px);
      font-weight: 700;
      border-radius: 8px;
      cursor: pointer;
      text-align: center;
      transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
    }
    .btn:hover {
      background: #e0f2fe;
      color: #0369a1;
      border-color: #7dd3fc;
    }
    .btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 5px rgba(2, 132, 199, 0.3);
    }

    /* Content Area */
    .flow-container {
      display: flex;
      flex-direction: column;
      gap: 7px;
      width: 100%;
      max-width: 380px;
      flex: 1;
      justify-content: center;
    }

    .card-row {
      background: #f8fafc;
      border: 1.5px solid #cbd5e1;
      border-radius: 10px;
      padding: 6px 10px;
      display: flex;
      align-items: center;
      opacity: 0.68;
      transition: opacity 0.25s ease, background 0.25s ease, border-color 0.25s ease, box-shadow 0.25s ease;
      min-height: 52px;
    }
    .card-row.active {
      opacity: 1;
      background: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 3px 10px rgba(2, 132, 199, 0.16);
    }
    .card-row.done {
      opacity: 0.88;
      background: #f1f5f9;
      border-color: #94a3b8;
    }

    .step-num {
      flex-shrink: 0;
      width: 22px;
      height: 22px;
      font-size: 11px;
      font-weight: 800;
      color: #475569;
      background: #e2e8f0;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      margin-right: 8px;
    }
    .card-row.active .step-num {
      background: #0284c7;
      color: #ffffff;
    }
    .card-row.done .step-num {
      background: #64748b;
      color: #ffffff;
    }

    .math-content {
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
      overflow: hidden;
    }

    /* Math typography */
    .math {
      font-size: clamp(12px, 3.6vw, 15px);
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
      flex-wrap: nowrap;
      gap: clamp(3px, 1.2vw, 6px);
      white-space: nowrap;
    }
    .frac {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      vertical-align: middle;
      padding: 0 2px;
      line-height: 1.15;
    }
    .num {
      border-bottom: 1.5px solid #1e293b;
      padding-bottom: 2px;
      width: 100%;
      text-align: center;
    }
    .den {
      padding-top: 2px;
      width: 100%;
      text-align: center;
    }

    /* Color coded math terms */
    .c-blue { color: #0369a1; }
    .c-amber { color: #b45309; }
    .c-green { color: #15803d; }
    .c-purple { color: #6d28d9; }
    .op { color: #475569; font-weight: 600; }

    /* Balance Scale Row */
    .balance-card {
      padding: 5px 8px;
      min-height: 66px;
    }
    .scale-wrapper {
      flex: 1;
      display: flex;
      justify-content: center;
      align-items: center;
      width: 100%;
    }
    .scale-svg {
      width: 100%;
      max-width: 280px;
      height: 56px;
    }

    /* Auto Play bar */
    .play-bar {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      max-width: 380px;
      margin-top: 6px;
      padding: 0 4px;
    }
    .play-btn {
      background: none;
      border: 1px solid #cbd5e1;
      background: #f8fafc;
      color: #334155;
      font-size: 12px;
      border-radius: 6px;
      padding: 4px 8px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
      font-weight: 600;
      transition: background 0.2s ease, border-color 0.2s ease;
    }
    .play-btn:hover {
      background: #e2e8f0;
      border-color: #94a3b8;
    }
    .reference-text {
      font-size: 12px;
      color: #475569;
      font-weight: 700;
      background: #f1f5f9;
      padding: 3px 8px;
      border-radius: 6px;
      border: 1px solid #e2e8f0;
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="btn active" onclick="setStep(0)">1. Ratio</button>
    <button class="btn" onclick="setStep(1)">2. Cross ×</button>
    <button class="btn" onclick="setStep(2)">3. Solve</button>
    <button class="btn" onclick="setStep(3)">4. Equal</button>
  </div>

  <div class="flow-container">
    
    <div class="card-row active" id="row-0">
      <span class="step-num">1</span>
      <div class="math-content">
        <div class="math">
          <div class="frac">
            <span class="num c-blue">1 kg</span>
            <span class="den c-amber">1000 g</span>
          </div>
          <span class="op">=</span>
          <div class="frac">
            <span class="num c-amber">k kg</span>
            <span class="den c-blue">450 g</span>
          </div>
        </div>
      </div>
    </div>

    
    <div class="card-row" id="row-1">
      <span class="step-num">2</span>
      <div class="math-content">
        <div class="math">
          <span class="c-amber">1000</span><span class="op">·</span><span class="c-amber">k</span>
          <span class="op">=</span>
          <span class="c-blue">1</span><span class="op">·</span><span class="c-blue">450</span>
          <span class="op">→</span>
          <span class="c-amber">1000k</span>
          <span class="op">=</span>
          <span class="c-blue">450</span>
        </div>
      </div>
    </div>

    
    <div class="card-row" id="row-2">
      <span class="step-num">3</span>
      <div class="math-content">
        <div class="math">
          <div class="frac">
            <span class="num">1000k</span>
            <span class="den c-purple">1000</span>
          </div>
          <span class="op">=</span>
          <div class="frac">
            <span class="num">450</span>
            <span class="den c-purple">1000</span>
          </div>
          <span class="op">→</span>
          <span class="c-green">k = 0.45 kg</span>
        </div>
      </div>
    </div>

    
    <div class="card-row balance-card" id="row-3">
      <span class="step-num">4</span>
      <div class="scale-wrapper">
        <svg class="scale-svg" viewBox="0 0 280 58">
          
          <line x1="140" y1="16" x2="140" y2="52" stroke="#475569" stroke-width="3" stroke-linecap="round"/>
          <line x1="116" y1="52" x2="164" y2="52" stroke="#334155" stroke-width="3.5" stroke-linecap="round"/>
          
          
          <polygon points="140,8 133,18 147,18" fill="#475569"/>
          
          
          <line x1="28" y1="16" x2="252" y2="16" stroke="#1e293b" stroke-width="3.5" stroke-linecap="round"/>
          
          
          <line x1="48" y1="16" x2="34" y2="36" stroke="#64748b" stroke-width="1.8"/>
          <line x1="48" y1="16" x2="62" y2="36" stroke="#64748b" stroke-width="1.8"/>
          <path d="M 28 36 C 28 47, 68 47, 68 36 Z" fill="#e2e8f0" stroke="#475569" stroke-width="2"/>
          
          <rect x="30" y="22" width="36" height="15" rx="3" fill="#0369a1" stroke="#0284c7" stroke-width="1"/>
          <text x="48" y="33.5" fill="#ffffff" font-size="11" font-weight="bold" font-family="system-ui, sans-serif" text-anchor="middle">450 g</text>

          
          <line x1="232" y1="16" x2="216" y2="36" stroke="#64748b" stroke-width="1.8"/>
          <line x1="232" y1="16" x2="248" y2="36" stroke="#64748b" stroke-width="1.8"/>
          <path d="M 212 36 C 212 47, 252 47, 252 36 Z" fill="#e2e8f0" stroke="#475569" stroke-width="2"/>
          
          <rect x="210" y="22" width="44" height="15" rx="3" fill="#15803d" stroke="#16a34a" stroke-width="1"/>
          <text x="232" y="33.5" fill="#ffffff" font-size="10.5" font-weight="bold" font-family="system-ui, sans-serif" text-anchor="middle">0.45 kg</text>
          
          
          <circle cx="140" cy="16" r="4.5" fill="#0284c7" stroke="#ffffff" stroke-width="1.5"/>
        </svg>
      </div>
    </div>
  </div>

  
  <div class="play-bar">
    <button class="play-btn" id="playToggle" onclick="togglePlay()">
      <span id="playIcon">⏸</span> <span id="playText">Auto</span>
    </button>
    <span class="reference-text">1 kg = 1000 g</span>
  </div>

  <script>
    let currentStep = 0;
    let playing = true;
    let timer = null;

    const rows = [
      document.getElementById('row-0'),
      document.getElementById('row-1'),
      document.getElementById('row-2'),
      document.getElementById('row-3')
    ];
    const buttons = document.querySelectorAll('.controls .btn');

    function updateView() {
      rows.forEach((row, i) => {
        row.classList.remove('active', 'done');
        if (i === currentStep) {
          row.classList.add('active');
        } else if (i < currentStep) {
          row.classList.add('done');
        }
      });

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

    function setStep(idx) {
      currentStep = idx;
      updateView();
      if (playing) restartTimer();
    }

    function nextStep() {
      currentStep = (currentStep + 1) % 4;
      updateView();
    }

    function restartTimer() {
      clearInterval(timer);
      timer = setInterval(nextStep, 3500);
    }

    function togglePlay() {
      playing = !playing;
      document.getElementById('playIcon').textContent = playing ? '⏸' : '▶';
      if (playing) {
        restartTimer();
      } else {
        clearInterval(timer);
      }
    }

    // Initialize auto play
    restartTimer();
  </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 {
      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: center;
      min-height: 100vh;
      padding: 16px;
    }
    .proportion-wrapper {
      width: 100%;
      max-width: 480px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    .banner {
      width: 100%;
      padding: 8px 14px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 700;
      text-align: center;
      letter-spacing: 0.2px;
    }
    .banner-top {
      background-color: #e0f2fe;
      border: 1.5px solid #7dd3fc;
      color: #0369a1;
    }
    .banner-bottom {
      background-color: #ffedd5;
      border: 1.5px solid #fdba74;
      color: #c2410c;
    }
    .equation-row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 12px;
    }
    .card-column {
      flex: 1;
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px 8px;
      display: flex;
      flex-direction: column;
      align-items: center;
      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.04);
    }
    .card-title {
      font-size: 12px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      margin-bottom: 10px;
    }
    .fraction {
      display: flex;
      flex-direction: column;
      align-items: center;
      width: 100%;
      max-width: 130px;
    }
    .unit-box {
      width: 100%;
      padding: 8px 4px;
      text-align: center;
      font-size: 18px;
      font-weight: 700;
      border-radius: 6px;
      transition: background-color 0.2s ease;
    }
    .unit-feet {
      color: #0284c7;
      background-color: #f0f9ff;
    }
    .unit-inches {
      color: #ea580c;
      background-color: #fff7ed;
    }
    .fraction-line {
      width: 80%;
      height: 3px;
      background-color: #1e2945;
      border-radius: 2px;
      margin: 6px 0;
    }
    .equals-sign {
      font-size: 32px;
      font-weight: 700;
      color: #1e2945;
      padding: 0 4px;
      user-select: none;
    }
  </style>
</head>
<body>
  <div class="proportion-wrapper">
    <div class="banner banner-top">Units must match: Feet</div>
    
    <div class="equation-row">
      <div class="card-column">
        <div class="card-title">Known Fact</div>
        <div class="fraction">
          <div class="unit-box unit-feet">1 foot</div>
          <div class="fraction-line"></div>
          <div class="unit-box unit-inches">12 inches</div>
        </div>
      </div>

      <div class="equals-sign">=</div>

      <div class="card-column">
        <div class="card-title">Your Problem</div>
        <div class="fraction">
          <div class="unit-box unit-feet">x feet</div>
          <div class="fraction-line"></div>
          <div class="unit-box unit-inches">54 inches</div>
        </div>
      </div>
    </div>

    <div class="banner banner-bottom">Units must match: Inches</div>
  </div>
</body>
</html>

111.26(b)(4)(H)

Aligned learning resources

Related diagrams