<!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: transparent;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }

    /* Stepper Controls */
    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
      width: 100%;
      max-width: 480px;
      justify-content: center;
      margin-bottom: 12px;
    }
    .step-btn {
      flex: 1;
      padding: 8px 10px;
      border: 1px solid #e2e8f0;
      background: #f8fafc;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
      cursor: pointer;
      text-align: center;
      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 Display Area */
    .card-area {
      width: 100%;
      max-width: 480px;
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 12px;
      justify-content: center;
    }

    /* Stage Tiles */
    .stages-row {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 8px;
    }
    .stage-card {
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 6px;
      text-align: center;
      transition: all 0.3s ease;
    }
    .stage-card.highlight {
      border-color: #0284c7;
      background: #f0f9ff;
    }
    .stage-icon {
      font-size: 22px;
      margin-bottom: 2px;
      display: block;
    }
    .stage-name {
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }
    .stage-count {
      font-size: 20px;
      font-weight: 800;
      color: #0f172a;
      margin-top: 2px;
    }

    /* Calculation Formula Box */
    .calc-box {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
      min-height: 120px;
      justify-content: center;
      box-shadow: 0 1px 3px rgba(0,0,0,0.04);
    }

    .formula-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      font-size: 20px;
      font-weight: 700;
      color: #334155;
    }
    .num-pill {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      min-width: 38px;
      height: 38px;
      padding: 0 8px;
      border-radius: 8px;
      background: #f1f5f9;
      color: #0f172a;
      transition: all 0.3s ease;
    }
    .num-pill.active-pill {
      background: #e0f2fe;
      color: #0369a1;
      border: 1px solid #7dd3fc;
    }
    .op {
      color: #94a3b8;
      font-weight: 600;
      font-size: 18px;
    }

    /* Sub-calculation breakdown */
    .sub-calc {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 14px;
      font-weight: 600;
      color: #64748b;
      opacity: 0;
      transform: translateY(4px);
      transition: all 0.3s ease;
    }
    .sub-calc.show {
      opacity: 1;
      transform: translateY(0);
    }

    /* Result Badge */
    .total-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      padding: 6px 16px;
      background: #0284c7;
      color: #ffffff;
      font-size: 18px;
      font-weight: 800;
      border-radius: 9999px;
      box-shadow: 0 3px 10px rgba(2, 132, 199, 0.3);
      opacity: 0;
      transform: scale(0.9);
      transition: all 0.3s ease;
    }
    .total-badge.show {
      opacity: 1;
      transform: scale(1);
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="step-btn active" id="btn0">1. Choices</button>
    <button class="step-btn" id="btn1">2. Multiply</button>
    <button class="step-btn" id="btn2">3. Total</button>
  </div>

  
  <div class="card-area">
    
    <div class="stages-row">
      <div class="stage-card highlight" id="cardMain">
        <span class="stage-icon">🍔</span>
        <div class="stage-name">Main</div>
        <div class="stage-count">4</div>
      </div>
      <div class="stage-card highlight" id="cardSide">
        <span class="stage-icon">🍟</span>
        <div class="stage-name">Side</div>
        <div class="stage-count">3</div>
      </div>
      <div class="stage-card highlight" id="cardDrink">
        <span class="stage-icon">🥤</span>
        <div class="stage-name">Drink</div>
        <div class="stage-count">5</div>
      </div>
    </div>

    
    <div class="calc-box">
      <div class="formula-row" id="formula">
        <span class="num-pill" id="pillMain">4</span>
        <span class="op">×</span>
        <span class="num-pill" id="pillSide">3</span>
        <span class="op">×</span>
        <span class="num-pill" id="pillDrink">5</span>
      </div>

      <div class="sub-calc" id="subCalc">
        <span>(4 × 3) = 12 combos</span>
        <span>→</span>
        <span>12 × 5</span>
      </div>

      <div class="total-badge" id="totalBadge">
        <span>60</span>
        <span style="font-size: 13px; font-weight: 600; opacity: 0.9;">Total Combos</span>
      </div>
    </div>
  </div>

  <script src="{{VENDOR_CDN}}/classace-diagram.js"></script>
  <script>
    const btn0 = document.getElementById('btn0');
    const btn1 = document.getElementById('btn1');
    const btn2 = document.getElementById('btn2');
    const buttons = [btn0, btn1, btn2];

    const cardMain = document.getElementById('cardMain');
    const cardSide = document.getElementById('cardSide');
    const cardDrink = document.getElementById('cardDrink');
    const stageCards = [cardMain, cardSide, cardDrink];

    const pillMain = document.getElementById('pillMain');
    const pillSide = document.getElementById('pillSide');
    const pillDrink = document.getElementById('pillDrink');
    const pills = [pillMain, pillSide, pillDrink];

    const subCalc = document.getElementById('subCalc');
    const totalBadge = document.getElementById('totalBadge');

    function renderStep(step) {
      buttons.forEach((btn, idx) => {
        btn.classList.toggle('active', idx === step);
      });

      if (step === 0) {
        // Stage 1: Focus on counting choices
        stageCards.forEach(c => c.classList.add('highlight'));
        pills.forEach(p => p.classList.remove('active-pill'));
        subCalc.classList.remove('show');
        totalBadge.classList.remove('show');
      } else if (step === 1) {
        // Stage 2: Multiply stages
        stageCards.forEach(c => c.classList.remove('highlight'));
        pills.forEach(p => p.classList.add('active-pill'));
        subCalc.classList.remove('show');
        totalBadge.classList.remove('show');
      } else if (step === 2) {
        // Stage 3: Step-by-step compute & final answer
        stageCards.forEach(c => c.classList.remove('highlight'));
        pills.forEach(p => p.classList.remove('active-pill'));
        subCalc.classList.add('show');
        totalBadge.classList.add('show');
      }
    }

    let currentStep = 0;
    let autoInterval = null;

    function setStep(idx) {
      currentStep = idx;
      renderStep(currentStep);
    }

    function startAutoPlay() {
      autoInterval = setInterval(() => {
        currentStep = (currentStep + 1) % 3;
        renderStep(currentStep);
      }, 3500);
    }

    function stopAutoPlay() {
      if (autoInterval) {
        clearInterval(autoInterval);
        autoInterval = null;
      }
    }

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

    // Start pedagogical auto-cycling
    renderStep(0);
    startAutoPlay();
  </script>
</body>
</html>

The Fundamental Counting Principle for Multi-Stage Experiments

<!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;
    }

    :root {
      --primary: #0284c7;
      --primary-light: #e0f2fe;
      --accent: #f59e0b;
      --accent-light: #fef3c7;
      --text: #1e293b;
      --muted: #64748b;
      --border: #cbd5e1;
      --panel-bg: #f8fafc;
    }

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

    .main-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
      max-width: 640px;
    }

    @media (max-width: 440px) {
      .main-grid {
        grid-template-columns: 1fr;
        gap: 10px;
      }
    }

    .scenario-card {
      background: var(--panel-bg);
      border: 1px solid var(--border);
      border-radius: 12px;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .scenario-title {
      font-size: 15px;
      font-weight: 700;
      margin-bottom: 12px;
      color: var(--text);
      text-align: center;
    }

    .slots-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      margin-bottom: 12px;
      width: 100%;
    }

    .slot-col {
      display: flex;
      flex-direction: column;
      align-items: center;
      flex: 1;
      max-width: 60px;
    }

    .slot-box {
      width: 100%;
      height: 48px;
      background: #ffffff;
      border: 2px solid var(--border);
      border-radius: 8px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 22px;
      font-weight: 800;
      color: var(--text);
      transition: all 0.3s ease;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
    }

    .slot-box.active {
      border-color: var(--primary);
      background: var(--primary-light);
      color: var(--primary);
      box-shadow: 0 0 0 3px rgba(2, 132, 199, 0.2);
    }

    .slot-tag {
      font-size: 11px;
      font-weight: 700;
      margin-top: 4px;
      height: 16px;
      color: var(--muted);
      white-space: nowrap;
    }

    .slot-tag.reduced {
      color: #ea580c;
    }

    .mult-sign {
      font-size: 16px;
      font-weight: 700;
      color: var(--muted);
      margin-bottom: 20px;
    }

    .pool-visual {
      display: flex;
      flex-wrap: wrap;
      gap: 3px;
      justify-content: center;
      background: #ffffff;
      border: 1px solid var(--border);
      border-radius: 6px;
      padding: 6px;
      margin-bottom: 12px;
      width: 100%;
      max-width: 190px;
      min-height: 42px;
      align-items: center;
    }

    .digit-pip {
      width: 16px;
      height: 16px;
      border-radius: 3px;
      background: #e2e8f0;
      color: #475569;
      font-size: 10px;
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: all 0.3s ease;
    }

    .digit-pip.used {
      background: #fed7aa;
      color: #9a3412;
      text-decoration: line-through;
      opacity: 0.45;
    }

    .digit-pip.selected {
      background: var(--primary);
      color: #ffffff;
      font-weight: 800;
    }

    .calc-box {
      font-size: 17px;
      font-weight: 800;
      color: var(--text);
      background: #ffffff;
      border: 1px solid var(--border);
      border-radius: 6px;
      padding: 6px 12px;
      width: 100%;
      text-align: center;
    }

    .calc-box .total {
      color: var(--primary);
      font-size: 20px;
    }

    .calc-box.no-rep .total {
      color: #d97706;
    }

    .controls-bar {
      display: flex;
      align-items: center;
      gap: 8px;
      margin-top: 10px;
    }

    .btn-step {
      background: #ffffff;
      border: 1px solid var(--border);
      border-radius: 6px;
      padding: 5px 12px;
      font-size: 13px;
      font-weight: 600;
      color: var(--text);
      cursor: pointer;
      transition: background 0.2s;
    }

    .btn-step.active {
      background: var(--primary);
      color: #ffffff;
      border-color: var(--primary);
    }

    .btn-play {
      background: var(--panel-bg);
      border: 1px solid var(--border);
      border-radius: 6px;
      padding: 5px 10px;
      font-size: 13px;
      cursor: pointer;
      font-weight: 600;
    }
  </style>
</head>
<body>

  <div class="main-grid">
    
    <div class="scenario-card">
      <div class="scenario-title">With Repetition</div>
      
      <div class="slots-row">
        <div class="slot-col">
          <div class="slot-box" id="rep-s1">9</div>
          <div class="slot-tag" id="rep-t1">Slot 1</div>
        </div>
        <div class="mult-sign">×</div>
        <div class="slot-col">
          <div class="slot-box" id="rep-s2">9</div>
          <div class="slot-tag" id="rep-t2">Slot 2</div>
        </div>
        <div class="mult-sign">×</div>
        <div class="slot-col">
          <div class="slot-box" id="rep-s3">9</div>
          <div class="slot-tag" id="rep-t3">Slot 3</div>
        </div>
      </div>

      <div class="pool-visual" id="rep-pool">
        
      </div>

      <div class="calc-box">
        9 × 9 × 9 = <span class="total">729</span>
      </div>
    </div>

    
    <div class="scenario-card">
      <div class="scenario-title">Without Repetition</div>
      
      <div class="slots-row">
        <div class="slot-col">
          <div class="slot-box" id="norep-s1">9</div>
          <div class="slot-tag" id="norep-t1">9 left</div>
        </div>
        <div class="mult-sign">×</div>
        <div class="slot-col">
          <div class="slot-box" id="norep-s2">8</div>
          <div class="slot-tag reduced" id="norep-t2">8 left</div>
        </div>
        <div class="mult-sign">×</div>
        <div class="slot-col">
          <div class="slot-box" id="norep-s3">7</div>
          <div class="slot-tag reduced" id="norep-t3">7 left</div>
        </div>
      </div>

      <div class="pool-visual" id="norep-pool">
        
      </div>

      <div class="calc-box no-rep">
        9 × 8 × 7 = <span class="total">504</span>
      </div>
    </div>
  </div>

  <div class="controls-bar">
    <button class="btn-play" id="playBtn">⏸</button>
    <button class="btn-step active" data-step="0">Slot 1</button>
    <button class="btn-step" data-step="1">Slot 2</button>
    <button class="btn-step" data-step="2">Slot 3</button>
    <button class="btn-step" data-step="3">All</button>
  </div>

  <script>
    const repPool = document.getElementById('rep-pool');
    const noRepPool = document.getElementById('norep-pool');
    const stepBtns = document.querySelectorAll('.btn-step');
    const playBtn = document.getElementById('playBtn');

    // Build digit pips 1..9
    function initPool(container, prefix) {
      container.innerHTML = '';
      for (let i = 1; i <= 9; i++) {
        const pip = document.createElement('div');
        pip.className = 'digit-pip';
        pip.id = `${prefix}-p${i}`;
        pip.textContent = i;
        container.appendChild(pip);
      }
    }

    initPool(repPool, 'rep');
    initPool(noRepPool, 'norep');

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

    function renderStep(step) {
      currentStep = step;

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

      // Slot highlights
      const repSlots = [document.getElementById('rep-s1'), document.getElementById('rep-s2'), document.getElementById('rep-s3')];
      const noRepSlots = [document.getElementById('norep-s1'), document.getElementById('norep-s2'), document.getElementById('norep-s3')];

      repSlots.forEach((slot, idx) => {
        slot.classList.toggle('active', step === 3 || step === idx);
      });
      noRepSlots.forEach((slot, idx) => {
        slot.classList.toggle('active', step === 3 || step === idx);
      });

      // Pool pips states
      // With Repetition: All 9 are always available; active slot picks '3'
      for (let i = 1; i <= 9; i++) {
        const p = document.getElementById(`rep-p${i}`);
        p.className = 'digit-pip';
        if (step === 0 && i === 3) p.className = 'digit-pip selected';
        if (step === 1 && i === 3) p.className = 'digit-pip selected';
        if (step === 2 && i === 3) p.className = 'digit-pip selected';
      }

      // Without Repetition:
      // Step 0: slot 1 picks 3 (9 available)
      // Step 1: 3 is locked used, slot 2 picks 7 (8 available)
      // Step 2: 3 and 7 locked used, slot 3 picks 2 (7 available)
      // Step 3: All 3 used shown locked
      for (let i = 1; i <= 9; i++) {
        const p = document.getElementById(`norep-p${i}`);
        p.className = 'digit-pip';

        if (step === 0) {
          if (i === 3) p.className = 'digit-pip selected';
        } else if (step === 1) {
          if (i === 3) p.className = 'digit-pip used';
          if (i === 7) p.className = 'digit-pip selected';
        } else if (step === 2) {
          if (i === 3 || i === 7) p.className = 'digit-pip used';
          if (i === 2) p.className = 'digit-pip selected';
        } else if (step === 3) {
          if (i === 3 || i === 7 || i === 2) p.className = 'digit-pip used';
        }
      }
    }

    function nextStep() {
      const next = (currentStep + 1) % 4;
      renderStep(next);
    }

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

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

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

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

    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">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    html, body {
      width: 100%;
      height: 100%;
      background: #ffffff;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      user-select: none;
      -webkit-user-select: none;
    }
    .main-wrap {
      width: 100%;
      height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 10px 12px 12px;
    }
    .math-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: 18px;
      font-weight: 700;
      padding: 6px 14px;
      background: #f8fafc;
      border-radius: 999px;
      border: 1px solid #e2e8f0;
    }
    .badge-s { color: #2563eb; background: #eff6ff; padding: 2px 8px; border-radius: 6px; }
    .badge-p { color: #d97706; background: #fef3c7; padding: 2px 8px; border-radius: 6px; }
    .badge-t { color: #059669; background: #ecfdf5; padding: 2px 10px; border-radius: 6px; border: 1px solid #a7f3d0; }
    .svg-container {
      width: 100%;
      flex: 1;
      min-height: 0;
      display: flex;
      justify-content: center;
      align-items: center;
    }
    svg {
      width: 100%;
      height: 100%;
      max-height: 350px;
    }
    .node-shirt { cursor: pointer; transition: opacity 0.25s ease; }
    .node-pants { transition: opacity 0.25s ease; }
    .node-out { transition: opacity 0.25s ease, transform 0.25s ease; }
    .branch-line { fill: none; stroke-width: 1.75; transition: stroke-opacity 0.25s ease, stroke 0.25s ease; }
    .dimmed { opacity: 0.18; }
    .dimmed-line { stroke-opacity: 0.12 !important; }
    .controls {
      display: flex;
      gap: 6px;
      flex-wrap: wrap;
      justify-content: center;
    }
    .btn-tab {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 8px;
      padding: 5px 12px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
    }
    .btn-tab.active {
      background: #1e2945;
      border-color: #1e2945;
      color: #ffffff;
    }
  </style>
</head>
<body>
  <div class="main-wrap">
    <div class="math-bar">
      <span class="badge-s" id="numS">3 Shirts</span>
      <span>×</span>
      <span class="badge-p" id="numP">4 Pants</span>
      <span>=</span>
      <span class="badge-t" id="numTotal">12 Outfits</span>
    </div>

    <div class="svg-container">
      <svg id="treeSvg" viewBox="0 0 540 330">
        <defs>
          <filter id="shadow" x="-10%" y="-10%" width="120%" height="120%">
            <feDropShadow dx="0" dy="1" stdDeviation="1.5" flood-opacity="0.08" />
          </filter>
        </defs>
        <g id="branches"></g>
        <g id="shirts"></g>
        <g id="pants"></g>
        <g id="outcomes"></g>
      </svg>
    </div>

    <div class="controls">
      <button class="btn-tab active" onclick="selectShirt(-1)">All (12)</button>
      <button class="btn-tab" onclick="selectShirt(0)">🔴 Red</button>
      <button class="btn-tab" onclick="selectShirt(1)">🔵 Blue</button>
      <button class="btn-tab" onclick="selectShirt(2)">🟢 Green</button>
    </div>
  </div>

  <script>
    const shirts = [
      { name: 'Red', color: '#ef4444', bg: '#fee2e2', stroke: '#f87171', icon: '🔴' },
      { name: 'Blue', color: '#2563eb', bg: '#dbeafe', stroke: '#60a5fa', icon: '🔵' },
      { name: 'Green', color: '#059669', bg: '#d1fae5', stroke: '#34d399', icon: '🟢' }
    ];

    const pants = [
      { name: 'Jeans', color: '#1e40af' },
      { name: 'Khakis', color: '#b45309' },
      { name: 'Shorts', color: '#0f766e' },
      { name: 'Sweats', color: '#475569' }
    ];

    const branchG = document.getElementById('branches');
    const shirtG = document.getElementById('shirts');
    const pantsG = document.getElementById('pants');
    const outG = document.getElementById('outcomes');

    const sX = 75;
    const pX = 250;
    const oX = 430;

    let activeShirt = -1;

    function buildTree() {
      branchG.innerHTML = '';
      shirtG.innerHTML = '';
      pantsG.innerHTML = '';
      outG.innerHTML = '';

      let outcomeIdx = 0;

      shirts.forEach((s, sIdx) => {
        const sy = 55 + sIdx * 105;

        // Shirt node
        const sGroup = document.createElementNS('http://www.w3.org/2000/svg', 'g');
        sGroup.setAttribute('class', `node-shirt s-grp-${sIdx}`);
        sGroup.setAttribute('onclick', `selectShirt(${sIdx})`);
        sGroup.innerHTML = `
          <rect x="${sX - 58}" y="${sy - 18}" width="95" height="36" rx="8" fill="${s.bg}" stroke="${s.stroke}" stroke-width="1.5" filter="url(#shadow)"/>
          <text x="${sX - 44}" y="${sy + 5}" font-size="14" font-weight="700" fill="${s.color}">${s.name}</text>
        `;
        shirtG.appendChild(sGroup);

        pants.forEach((p, pIdx) => {
          const py = 22 + (sIdx * 4 + pIdx) * 25.8;

          // Branch line: Shirt -> Pants
          const path1 = document.createElementNS('http://www.w3.org/2000/svg', 'path');
          const d1 = `M ${sX + 37} ${sy} C ${sX + 110} ${sy}, ${pX - 90} ${py}, ${pX - 50} ${py}`;
          path1.setAttribute('d', d1);
          path1.setAttribute('class', `branch-line line-s-${sIdx}`);
          path1.setAttribute('stroke', s.stroke);
          branchG.appendChild(path1);

          // Pants node
          const pGroup = document.createElementNS('http://www.w3.org/2000/svg', 'g');
          pGroup.setAttribute('class', `node-pants p-grp-${sIdx}`);
          pGroup.innerHTML = `
            <rect x="${pX - 48}" y="${py - 10.5}" width="82" height="21" rx="5" fill="#f8fafc" stroke="#cbd5e1" stroke-width="1"/>
            <text x="${pX - 7}" y="${py + 4}" font-size="11" font-weight="600" fill="${p.color}" text-anchor="middle">${p.name}</text>
          `;
          pantsG.appendChild(pGroup);

          // Branch line: Pants -> Outcome
          const path2 = document.createElementNS('http://www.w3.org/2000/svg', 'path');
          const d2 = `M ${pX + 34} ${py} L ${oX - 42} ${py}`;
          path2.setAttribute('d', d2);
          path2.setAttribute('class', `branch-line line-s-${sIdx}`);
          path2.setAttribute('stroke', '#cbd5e1');
          branchG.appendChild(path2);

          // Final Outcome node
          outcomeIdx++;
          const oGroup = document.createElementNS('http://www.w3.org/2000/svg', 'g');
          oGroup.setAttribute('class', `node-out o-grp-${sIdx}`);
          oGroup.innerHTML = `
            <rect x="${oX - 40}" y="${py - 10.5}" width="125" height="21" rx="5" fill="#f1f5f9" stroke="#e2e8f0" stroke-width="1"/>
            <circle cx="${oX - 28}" cy="${py}" r="4" fill="${s.color}" />
            <text x="${oX - 18}" y="${py + 3.5}" font-size="10.5" font-weight="600" fill="#334155">${s.name.charAt(0)} + ${p.name}</text>
            <text x="${oX + 72}" y="${py + 3.5}" font-size="9.5" font-weight="700" fill="#94a3b8">#${outcomeIdx}</text>
          `;
          outG.appendChild(oGroup);
        });
      });
    }

    function selectShirt(idx) {
      activeShirt = idx;

      // Update buttons
      const btns = document.querySelectorAll('.btn-tab');
      btns.forEach((b, i) => {
        b.classList.toggle('active', (idx === -1 && i === 0) || (idx === i - 1));
      });

      // Update formula bar text
      const totalBadge = document.getElementById('numTotal');
      const numS = document.getElementById('numS');

      if (idx === -1) {
        numS.textContent = '3 Shirts';
        totalBadge.textContent = '12 Outfits';
      } else {
        numS.textContent = '1 Shirt (' + shirts[idx].name + ')';
        totalBadge.textContent = '4 Outfits';
      }

      // Update node styles
      shirts.forEach((_, sIdx) => {
        const isDim = (idx !== -1 && idx !== sIdx);
        document.querySelectorAll(`.s-grp-${sIdx}`).forEach(el => el.classList.toggle('dimmed', isDim));
        document.querySelectorAll(`.p-grp-${sIdx}`).forEach(el => el.classList.toggle('dimmed', isDim));
        document.querySelectorAll(`.o-grp-${sIdx}`).forEach(el => el.classList.toggle('dimmed', isDim));
        document.querySelectorAll(`.line-s-${sIdx}`).forEach(el => el.classList.toggle('dimmed-line', isDim));
      });
    }

    buildTree();
  </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>Fundamental Counting Principle - Slot Method</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      -webkit-tap-highlight-color: transparent;
    }

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

    .diagram {
      width: 100%;
      max-width: 620px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 20px;
    }

    /* Slots Grid / Flex Container */
    .slots-row {
      display: flex;
      align-items: center;
      justify-content: center;
      width: 100%;
      gap: 6px;
      flex-wrap: nowrap;
    }

    .slot-card {
      flex: 1;
      min-width: 68px;
      max-width: 110px;
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 4px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      cursor: pointer;
      transition: border-color 0.25s ease, background-color 0.25s ease, box-shadow 0.25s ease;
    }

    .slot-card.active {
      border-color: #0284c7;
      background: #f0f9ff;
      box-shadow: 0 0 0 3px rgba(2, 132, 199, 0.18);
    }

    .slot-stage {
      font-size: 11px;
      font-weight: 700;
      color: #64748b;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      margin-bottom: 2px;
    }

    .slot-icon {
      font-size: 24px;
      line-height: 1.2;
      margin-bottom: 2px;
    }

    .slot-name {
      font-size: 13px;
      font-weight: 600;
      color: #334155;
    }

    .slot-val {
      margin-top: 4px;
      font-size: 22px;
      font-weight: 800;
      color: #0369a1;
      line-height: 1;
      background: #e0f2fe;
      padding: 4px 10px;
      border-radius: 8px;
      border: 1px solid #bae6fd;
    }

    .slot-card.active .slot-val {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
    }

    .op-mult {
      font-size: 20px;
      font-weight: 900;
      color: #94a3b8;
      display: flex;
      align-items: center;
      justify-content: center;
      padding: 0 2px;
    }

    /* Calculation & Result Panel */
    .calc-box {
      width: 100%;
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 14px;
      padding: 16px 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }

    .formula-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: 18px;
      font-weight: 700;
      color: #475569;
      flex-wrap: wrap;
    }

    .f-num {
      padding: 2px 8px;
      border-radius: 6px;
      background: #e2e8f0;
      color: #1e2945;
      transition: all 0.25s ease;
    }

    .f-num.lit {
      background: #0284c7;
      color: #ffffff;
    }

    .f-sym {
      color: #94a3b8;
      font-weight: 900;
    }

    .result-badge {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      background: linear-gradient(135deg, #0284c7, #0369a1);
      color: #ffffff;
      border-radius: 10px;
      padding: 8px 24px;
      box-shadow: 0 4px 12px rgba(2, 132, 199, 0.25);
    }

    .result-number {
      font-size: 32px;
      font-weight: 900;
      line-height: 1.1;
      letter-spacing: -0.5px;
    }

    .result-label {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.8px;
      opacity: 0.95;
    }

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

    .step-btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 6px 14px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 700;
      cursor: pointer;
      transition: all 0.2s ease;
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .step-btn:hover {
      background: #f1f5f9;
      border-color: #94a3b8;
    }

    .step-btn.active-btn {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
    }

    @media (max-width: 420px) {
      .slot-stage { font-size: 9px; }
      .slot-name { font-size: 11px; }
      .slot-icon { font-size: 20px; }
      .slot-val { font-size: 18px; padding: 2px 6px; }
      .op-mult { font-size: 16px; }
      .result-number { font-size: 26px; }
      .result-label { font-size: 11px; }
      .formula-row { font-size: 15px; }
    }
  </style>
</head>
<body>

  <div class="diagram">
    
    <div class="slots-row">
      <div class="slot-card active" data-step="0" onclick="goToStep(0)">
        <span class="slot-stage">Stage 1</span>
        <span class="slot-icon">👕</span>
        <span class="slot-name">Shirts</span>
        <span class="slot-val">3</span>
      </div>

      <div class="op-mult">×</div>

      <div class="slot-card active" data-step="1" onclick="goToStep(1)">
        <span class="slot-stage">Stage 2</span>
        <span class="slot-icon">👖</span>
        <span class="slot-name">Pants</span>
        <span class="slot-val">4</span>
      </div>

      <div class="op-mult">×</div>

      <div class="slot-card active" data-step="2" onclick="goToStep(2)">
        <span class="slot-stage">Stage 3</span>
        <span class="slot-icon">👟</span>
        <span class="slot-name">Shoes</span>
        <span class="slot-val">6</span>
      </div>

      <div class="op-mult">×</div>

      <div class="slot-card active" data-step="3" onclick="goToStep(3)">
        <span class="slot-stage">Stage 4</span>
        <span class="slot-icon">🧢</span>
        <span class="slot-name">Hats</span>
        <span class="slot-val">5</span>
      </div>
    </div>

    
    <div class="calc-box">
      <div class="formula-row">
        <span class="f-num lit" id="fn0">3</span>
        <span class="f-sym">×</span>
        <span class="f-num lit" id="fn1">4</span>
        <span class="f-sym">×</span>
        <span class="f-num lit" id="fn2">6</span>
        <span class="f-sym">×</span>
        <span class="f-num lit" id="fn3">5</span>
        <span class="f-sym">=</span>
        <span class="f-sym" style="color: #0284c7; font-size: 20px;">360</span>
      </div>

      <div class="result-badge">
        <div class="result-number" id="resNumber">360</div>
        <div class="result-label" id="resLabel">Total Outfits</div>
      </div>
    </div>

    
    <div class="controls">
      <button class="step-btn" id="b0" onclick="setMultiplierStep(0)">Stage 1</button>
      <button class="step-btn" id="b1" onclick="setMultiplierStep(1)">Stage 1–2</button>
      <button class="step-btn" id="b2" onclick="setMultiplierStep(2)">Stage 1–3</button>
      <button class="step-btn active-btn" id="b3" onclick="setMultiplierStep(3)">All Stages</button>
    </div>
  </div>

  <script>
    const stages = [
      { val: 3, running: 3, label: '3 Combinations' },
      { val: 4, running: 12, label: '12 Combinations' },
      { val: 6, running: 72, label: '72 Combinations' },
      { val: 5, running: 360, label: '360 Total Outfits' }
    ];

    let currentStep = 3;

    function setMultiplierStep(stepIndex) {
      currentStep = stepIndex;
      const cards = document.querySelectorAll('.slot-card');
      const fNums = [
        document.getElementById('fn0'),
        document.getElementById('fn1'),
        document.getElementById('fn2'),
        document.getElementById('fn3')
      ];
      const btns = [
        document.getElementById('b0'),
        document.getElementById('b1'),
        document.getElementById('b2'),
        document.getElementById('b3')
      ];

      cards.forEach((card, idx) => {
        if (idx <= stepIndex) {
          card.classList.add('active');
        } else {
          card.classList.remove('active');
        }
      });

      fNums.forEach((fn, idx) => {
        if (idx <= stepIndex) {
          fn.classList.add('lit');
        } else {
          fn.classList.remove('lit');
        }
      });

      btns.forEach((btn, idx) => {
        if (idx === stepIndex) {
          btn.classList.add('active-btn');
        } else {
          btn.classList.remove('active-btn');
        }
      });

      const resNum = document.getElementById('resNumber');
      const resLbl = document.getElementById('resLabel');

      resNum.textContent = stages[stepIndex].running;
      resLbl.textContent = stages[stepIndex].label;
    }

    function goToStep(idx) {
      setMultiplierStep(idx);
    }
  </script>
</body>
</html>

Using Systematic Organized Lists for Compound Sample Spaces

Using Two-Way Grids and Tables to Find Sample Spaces

Constructing Two-Way Frequency Tables from Data

Constructing Tree Diagrams for Independent Events

Constructing Tree Diagrams for Dependent Events Without Replacement

Calculating Compound And and Or Probabilities from Tree Diagrams

Simulating Compound Events with Random Numbers and Digital Tools

math

Compound Probability, Tree Diagrams, and Counting Principles

确定性事件（必然事件、不可能事件）与随机事件

概率的数学定义与取值范围（0到1之间）

等可能事件（古典概型）的特征与概率公式

一步实验的直接列举法求概率（摸球、掷骰子、抽牌）

两步（两因素）试验的列表法列举与概率求解

树状图（分枝图）的画法与样本空间列举

三步及多步复合试验的树状图概率求解

“放回抽样”与“不放回抽样”概率模型的对比辨析

基于概率计算的博弈游戏公平性判断与规则设计

几何概型初步：转盘与面积型等可能概率

随机事件与概率计算（列表法与树状图）

社会调研案例：社区生活垃圾分类现状与减量化数学分析

城市交通案例：公交站点候车时间与排队服务系统优化

经济生活案例：商场促销方案与抽奖期望收益评估

体育健康案例：青少年体质健康多项指标的综合评定与聚类

科技前沿案例：家庭碳足迹核算与节能减排趋势预测模型

综合实践探究成果展示、同行互评与深度反思

综合与实践：数据建模与社会生活决策

Listas sistemáticas y tablas de doble entrada para conteo

Diagramas de árbol para conteo

Principio fundamental del conteo: regla del producto

Permutaciones simples: orden en las agrupaciones

Combinaciones simples: cuando el orden no importa

Resolución de problemas combinatorios en contextos cotidianos

Exploración de patrones numéricos con calculadora

Conjeturas sobre divisibilidad y primos usando tecnología

Elección del método de cálculo: mental, escrito o digital

Conteo combinatorio y herramientas tecnológicas

Distinción entre fenómenos deterministas y aleatorios

Espacio muestral y tipos de eventos: seguro, posible e imposible

Diagramas de árbol para predecir posibilidades en experimentos compuestos

Cálculo de la probabilidad clásica: regla de Laplace

Probabilidad como fracción, decimal y porcentaje

Probabilidad frecuencial y simulación de experimentos

Conjeturas y toma de decisiones en juegos de azar

Probabilidad y experimentos aleatorios

Representing Sample Spaces with Lists

Representing Sample Spaces with Tree Diagrams

Using Tree Diagrams to Calculate Compound Probabilities

Selecting Simulations for Simple Events

Selecting Simulations for Compound Events

Using Technology for Probability Simulations

Determining Experimental Probabilities from Simulations

Probability: Sample Spaces and Simulations

Making Predictions Using Experimental Data

Making Predictions Using Theoretical Probability

Comparing Experimental and Theoretical Compound Probabilities

Probability of a Simple Event and Its Complement

Describing the Relationship Between an Event and Its Complement

Comparing Simple and Compound Event Probabilities

Probability: Predictions and Complements

Qualitative Predictions from Simple Experiments

Quantitative Predictions and Comparisons from Experiments

Determining Experimental and Theoretical Probabilities

Project: Collecting Real-Life Situations Corresponding to Different Probabilities

Probability: Real-World Predictions and Applications

OGM.8.SP.6

OGM.8.SP.6

Aligned learning resources

Related diagrams