<!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, sans-serif;
      background: #f8fafc;
      color: #1e293b;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      max-height: 600px;
      padding: 12px 16px;
      user-select: none;
      -webkit-user-select: none;
      overflow-x: hidden;
    }

    /* Stepper Header */
    .step-nav {
      display: flex;
      align-items: center;
      gap: 8px;
      margin-bottom: 6px;
    }

    .dot {
      width: 28px;
      height: 6px;
      border-radius: 999px;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.3s ease, transform 0.2s ease;
    }

    .dot.active {
      background: #2563eb;
      transform: scaleY(1.33);
    }

    /* Main Stage */
    .stage {
      width: 100%;
      max-width: 440px;
      flex: 1;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      position: relative;
      gap: 12px;
    }

    /* Transfer Arc Canvas / Layer */
    .transfer-bar {
      width: 100%;
      height: 32px;
      position: relative;
      display: flex;
      justify-content: center;
      align-items: center;
      opacity: 0;
      transform: translateY(4px);
      transition: opacity 0.3s ease, transform 0.3s ease;
    }

    .transfer-bar.visible {
      opacity: 1;
      transform: translateY(0);
    }

    .transfer-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: #eff6ff;
      border: 1.5px dashed #2563eb;
      color: #1d4ed8;
      font-weight: 700;
      font-size: 13px;
      padding: 3px 12px;
      border-radius: 999px;
      white-space: nowrap;
    }

    .transfer-arrow {
      font-size: 15px;
      line-height: 1;
    }

    /* Equation Rows */
    .equation-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: clamp(4px, 2vw, 10px);
      width: 100%;
      max-width: 100%;
      transition: opacity 0.4s ease, filter 0.4s ease;
    }

    .num-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-width: 68px;
      max-width: 100px;
      flex: 1 1 0;
      padding: 8px 6px;
      background: #ffffff;
      border-radius: 10px;
      border: 2px solid #e2e8f0;
      box-shadow: 0 2px 5px rgba(0, 0, 0, 0.04);
      position: relative;
      transition: all 0.3s ease;
    }

    .num-value {
      font-size: clamp(20px, 5.5vw, 26px);
      font-weight: 800;
      color: #0f172a;
      letter-spacing: -0.5px;
      line-height: 1.2;
    }

    .badge-shift {
      position: absolute;
      top: -11px;
      font-size: 11px;
      font-weight: 800;
      padding: 1px 6px;
      border-radius: 999px;
      opacity: 0;
      transform: translateY(3px);
      transition: opacity 0.3s ease, transform 0.3s ease;
      white-space: nowrap;
    }

    .badge-add {
      background: #dbeafe;
      color: #1d4ed8;
      right: 4px;
    }

    .badge-sub {
      background: #fee2e2;
      color: #b91c1c;
      left: 4px;
    }

    .show-shift .badge-shift {
      opacity: 1;
      transform: translateY(0);
    }

    .num-box.friendly {
      background: #f0fdf4;
      border-color: #86efac;
    }

    .num-box.friendly .num-value {
      color: #15803d;
    }

    .num-box.target {
      background: #eff6ff;
      border-color: #93c5fd;
    }

    .num-box.target .num-value {
      color: #1d4ed8;
    }

    .operator {
      font-size: clamp(18px, 5vw, 24px);
      font-weight: 800;
      color: #475569;
      flex-shrink: 0;
      min-width: 14px;
      text-align: center;
      transition: opacity 0.3s ease;
    }

    /* Transform Indicator */
    .arrow-divider {
      display: flex;
      align-items: center;
      justify-content: center;
      color: #64748b;
      font-size: 20px;
      font-weight: 800;
      opacity: 0;
      transform: translateY(-4px);
      transition: opacity 0.3s ease, transform 0.3s ease;
      height: 16px;
    }

    .arrow-divider.visible {
      opacity: 1;
      transform: translateY(0);
    }

    /* Sum Box */
    .sum-box {
      min-width: 68px;
      max-width: 100px;
      flex: 1 1 0;
      padding: 8px 6px;
      background: #16a34a;
      color: #ffffff;
      border-radius: 10px;
      font-size: clamp(20px, 5.5vw, 26px);
      font-weight: 800;
      text-align: center;
      line-height: 1.2;
      box-shadow: 0 4px 10px rgba(22, 163, 74, 0.25);
      opacity: 0;
      transform: scale(0.9);
      transition: opacity 0.4s ease, transform 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
    }

    .sum-box.visible {
      opacity: 1;
      transform: scale(1);
    }

    /* Inactive preview state with accessible contrast (>= 3:1 ratio) */
    .row-inactive {
      opacity: 0.55;
    }

    .row-active {
      opacity: 1;
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      margin-top: 6px;
      width: 100%;
    }

    .btn {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      padding: 7px 14px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #334155;
      cursor: pointer;
      transition: background-color 0.2s ease, border-color 0.2s ease;
    }

    .btn:active {
      background: #f1f5f9;
    }

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

    .btn-primary:active {
      background: #1d4ed8;
    }
  </style>
</head>
<body>

  
  <div class="step-nav" id="stepNav">
    <div class="dot active" onclick="goToStep(0)" title="Step 1"></div>
    <div class="dot" onclick="goToStep(1)" title="Step 2"></div>
    <div class="dot" onclick="goToStep(2)" title="Step 3"></div>
    <div class="dot" onclick="goToStep(3)" title="Step 4"></div>
  </div>

  
  <div class="stage">

    
    <div class="transfer-bar" id="transferBar">
      <div class="transfer-badge">
        <span>Give 2</span>
        <span class="transfer-arrow">⇠</span>
        <span>Take 2</span>
      </div>
    </div>

    
    <div class="equation-row" id="rowOriginal">
      <div class="num-box" id="box398">
        <span class="badge-shift badge-add">+2</span>
        <span class="num-value">398</span>
      </div>

      <span class="operator">+</span>

      <div class="num-box" id="box145">
        <span class="badge-shift badge-sub">-2</span>
        <span class="num-value">145</span>
      </div>
    </div>

    
    <div class="arrow-divider" id="transformArrow">↓</div>

    
    <div class="equation-row row-inactive" id="rowTransformed">
      <div class="num-box" id="box400">
        <span class="num-value">400</span>
      </div>

      <span class="operator">+</span>

      <div class="num-box" id="box143">
        <span class="num-value">143</span>
      </div>

      <span class="operator" id="eqSign" style="opacity: 0.55;">=</span>

      <div class="sum-box" id="box543">543</div>
    </div>

  </div>

  
  <div class="controls">
    <button class="btn" id="prevBtn" onclick="step(-1)">‹ Back</button>
    <button class="btn btn-primary" id="playBtn" onclick="togglePlay()">⏸ Pause</button>
    <button class="btn" id="nextBtn" onclick="step(1)">Next ›</button>
  </div>

  <script>
    let currentStep = 0;
    const totalSteps = 4;
    let timer = null;
    let isPlaying = true;

    const dots = document.querySelectorAll('.dot');
    const transferBar = document.getElementById('transferBar');
    const box398 = document.getElementById('box398');
    const box145 = document.getElementById('box145');
    const transformArrow = document.getElementById('transformArrow');
    const rowTransformed = document.getElementById('rowTransformed');
    const box400 = document.getElementById('box400');
    const box143 = document.getElementById('box143');
    const eqSign = document.getElementById('eqSign');
    const box543 = document.getElementById('box543');
    const playBtn = document.getElementById('playBtn');

    function renderStep(idx) {
      currentStep = idx;

      // Update dots
      dots.forEach((dot, i) => {
        dot.classList.toggle('active', i === idx);
      });

      // Reset base classes
      transferBar.classList.remove('visible');
      box398.classList.remove('show-shift', 'target');
      box145.classList.remove('show-shift');
      transformArrow.classList.remove('visible');
      rowTransformed.classList.remove('row-active');
      rowTransformed.classList.add('row-inactive');
      box400.classList.remove('target');
      box143.classList.remove('friendly');
      eqSign.style.opacity = '0.55';
      box543.classList.remove('visible');

      // Apply step-specific visuals
      if (idx === 0) {
        // Step 1: Base problem
        rowTransformed.classList.add('row-inactive');
      } else if (idx === 1) {
        // Step 2: Transfer 2 from 145 to 398
        transferBar.classList.add('visible');
        box398.classList.add('show-shift', 'target');
        box145.classList.add('show-shift');
      } else if (idx === 2) {
        // Step 3: Transformed friendly problem
        transferBar.classList.add('visible');
        box398.classList.add('show-shift');
        box145.classList.add('show-shift');
        transformArrow.classList.add('visible');
        rowTransformed.classList.remove('row-inactive');
        rowTransformed.classList.add('row-active');
        box400.classList.add('target');
        box143.classList.add('friendly');
      } else if (idx === 3) {
        // Step 4: Final sum
        transformArrow.classList.add('visible');
        rowTransformed.classList.remove('row-inactive');
        rowTransformed.classList.add('row-active');
        box400.classList.add('target');
        box143.classList.add('friendly');
        eqSign.style.opacity = '1';
        box543.classList.add('visible');
      }
    }

    function goToStep(idx) {
      renderStep(idx);
      resetTimer();
    }

    function step(dir) {
      let next = (currentStep + dir + totalSteps) % totalSteps;
      goToStep(next);
    }

    function togglePlay() {
      isPlaying = !isPlaying;
      playBtn.textContent = isPlaying ? '⏸ Pause' : '▶ Play';
      if (isPlaying) {
        startTimer();
      } else {
        clearInterval(timer);
      }
    }

    function startTimer() {
      clearInterval(timer);
      timer = setInterval(() => {
        let next = (currentStep + 1) % totalSteps;
        renderStep(next);
      }, 3500);
    }

    function resetTimer() {
      if (isPlaying) {
        startTimer();
      }
    }

    // Initialize
    renderStep(0);
    startTimer();
  </script>
</body>
</html>

Mental Addition Strategies for Multi-Digit Numbers

<!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: #f8fafc;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }

    .header-bar {
      width: 100%;
      max-width: 440px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      background: #ffffff;
      padding: 10px 16px;
      border-radius: 12px;
      border: 1px solid #e2e8f0;
      box-shadow: 0 1px 3px rgba(0,0,0,0.04);
    }

    .problem-label {
      font-size: 18px;
      font-weight: 700;
      color: #1e2945;
    }

    .final-badge {
      background: #ecfdf5;
      color: #059669;
      border: 1px solid #a7f3d0;
      padding: 4px 12px;
      border-radius: 20px;
      font-size: 14px;
      font-weight: 700;
      letter-spacing: 0.2px;
      transition: opacity 0.3s ease;
    }

    .steps-container {
      width: 100%;
      max-width: 440px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      margin: 12px 0;
      position: relative;
    }

    .step-card {
      background: #ffffff;
      border: 2px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px 16px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      transition: all 0.3s ease;
      cursor: pointer;
      opacity: 0.45;
    }

    .step-card.active {
      opacity: 1;
      border-color: #22b7ff;
      box-shadow: 0 4px 12px rgba(34, 183, 255, 0.15);
      transform: translateY(-1px);
    }

    .step-left {
      display: flex;
      align-items: center;
      gap: 12px;
    }

    .step-num {
      width: 28px;
      height: 28px;
      border-radius: 50%;
      background: #f1f5f9;
      color: #64748b;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 14px;
      font-weight: 700;
      transition: all 0.3s ease;
    }

    .step-card.active .step-num {
      background: #22b7ff;
      color: #ffffff;
    }

    .step-info {
      display: flex;
      flex-direction: column;
      gap: 2px;
    }

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

    .step-card.active .step-title {
      color: #0284c7;
    }

    .step-math {
      font-size: 18px;
      font-weight: 700;
      color: #1e2945;
      font-variant-numeric: tabular-nums;
    }

    .tag-bubble {
      font-size: 13px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 8px;
      font-variant-numeric: tabular-nums;
    }

    .tag-blue {
      background: #e0f2fe;
      color: #0284c7;
      border: 1px solid #bae6fd;
    }

    .tag-orange {
      background: #fff7ed;
      color: #ea580c;
      border: 1px solid #ffedd5;
    }

    .tag-green {
      background: #ecfdf5;
      color: #059669;
      border: 1px solid #a7f3d0;
    }

    .connector-arrow {
      align-self: center;
      color: #94a3b8;
      font-size: 14px;
      line-height: 1;
      margin: -4px 0;
    }

    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 6px 14px;
      border-radius: 8px;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
      transition: background 0.2s, border-color 0.2s;
    }

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

    .btn:active {
      background: #e2e8f0;
    }

    .dots {
      display: flex;
      gap: 6px;
      margin-left: 8px;
    }

    .dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s, transform 0.2s;
    }

    .dot.active {
      background: #22b7ff;
      transform: scale(1.2);
    }
  </style>
</head>
<body>

  <div class="header-bar">
    <div class="problem-label">564 + 199</div>
    <div class="final-badge" id="finalBadge">Answer: 763</div>
  </div>

  <div class="steps-container">
    
    <div class="step-card active" id="stepCard0" onclick="goToStep(0)">
      <div class="step-left">
        <div class="step-num">1</div>
        <div class="step-info">
          <div class="step-title">Round Up</div>
          <div class="step-math">199 ➔ 200</div>
        </div>
      </div>
      <div class="tag-bubble tag-blue">+1</div>
    </div>

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

    
    <div class="step-card" id="stepCard1" onclick="goToStep(1)">
      <div class="step-left">
        <div class="step-num">2</div>
        <div class="step-info">
          <div class="step-title">Easy Add</div>
          <div class="step-math">564 + 200</div>
        </div>
      </div>
      <div class="tag-bubble tag-orange">= 764</div>
    </div>

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

    
    <div class="step-card" id="stepCard2" onclick="goToStep(2)">
      <div class="step-left">
        <div class="step-num">3</div>
        <div class="step-info">
          <div class="step-title">Adjust</div>
          <div class="step-math">764 − 1</div>
        </div>
      </div>
      <div class="tag-bubble tag-green">= 763</div>
    </div>
  </div>

  <div class="controls">
    <button class="btn" id="prevBtn" onclick="prevStep()">◀</button>
    <button class="btn" id="playBtn" onclick="togglePlay()">⏸</button>
    <button class="btn" id="nextBtn" onclick="nextStep()">▶</button>
    <div class="dots">
      <div class="dot active" onclick="goToStep(0)"></div>
      <div class="dot" onclick="goToStep(1)"></div>
      <div class="dot" onclick="goToStep(2)"></div>
    </div>
  </div>

  <script>
    let currentStep = 0;
    let isPlaying = true;
    let intervalId = null;

    const cards = [
      document.getElementById('stepCard0'),
      document.getElementById('stepCard1'),
      document.getElementById('stepCard2')
    ];
    const dots = document.querySelectorAll('.dot');
    const playBtn = document.getElementById('playBtn');
    const badge = document.getElementById('finalBadge');

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

      dots.forEach((dot, idx) => {
        if (idx === currentStep) {
          dot.classList.add('active');
        } else {
          dot.classList.remove('active');
        }
      });

      if (currentStep === 2) {
        badge.style.opacity = '1';
        badge.style.transform = 'scale(1.04)';
      } else {
        badge.style.opacity = '0.7';
        badge.style.transform = 'scale(1)';
      }
    }

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

    function nextStep() {
      currentStep = (currentStep + 1) % cards.length;
      updateView();
    }

    function prevStep() {
      currentStep = (currentStep - 1 + cards.length) % cards.length;
      updateView();
    }

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

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

    function togglePlay() {
      if (isPlaying) {
        stopAutoPlay();
      } else {
        startAutoPlay();
      }
    }

    // Initialize
    updateView();
    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;
      user-select: none;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }
    .header-calc {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: 20px;
      font-weight: 700;
      margin-top: 4px;
      margin-bottom: 8px;
    }
    .badge {
      display: inline-flex;
      align-items: center;
      padding: 4px 10px;
      border-radius: 8px;
      font-size: 14px;
      font-weight: 600;
    }
    .b-blue { background: #e0f2fe; color: #0284c7; }
    .b-green { background: #dcfce7; color: #15803d; }
    .b-purple { background: #ede9fe; color: #7c3aed; }
    .b-sum { background: #f1f5f9; color: #0f172a; border: 1px solid #cbd5e1; }

    .chart-container {
      width: 100%;
      max-width: 580px;
      position: relative;
      margin: 12px 0;
    }
    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }

    .jump-arc {
      fill: none;
      stroke-width: 3.5;
      stroke-linecap: round;
      transition: opacity 0.35s ease, stroke-dashoffset 0.5s ease;
    }
    .arc-1 { stroke: #0284c7; }
    .arc-2 { stroke: #16a34a; }
    .arc-3 { stroke: #7c3aed; }

    .tag {
      font-size: 13px;
      font-weight: 700;
      text-anchor: middle;
      transition: opacity 0.35s ease, transform 0.35s ease;
    }
    .tag-1 { fill: #0284c7; }
    .tag-2 { fill: #15803d; }
    .tag-3 { fill: #7c3aed; }

    .milestone-num {
      font-size: 15px;
      font-weight: 800;
      text-anchor: middle;
      fill: #1e2945;
      transition: opacity 0.35s ease;
    }
    .landmark {
      fill: #15803d;
    }

    .stepper-controls {
      display: flex;
      flex-wrap: wrap;
      gap: 8px;
      justify-content: center;
      margin-top: 4px;
      width: 100%;
      max-width: 540px;
    }
    .step-btn {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      color: #475569;
      font-size: 13px;
      font-weight: 600;
      padding: 7px 14px;
      border-radius: 20px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background 0.2s, color 0.2s, box-shadow 0.2s;
    }
    .step-btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.3);
    }
    .step-btn:active {
      transform: translateY(1px);
    }
  </style>
</head>
<body>

  
  <div class="header-calc">
    <span>347 + 285 =</span>
    <span class="badge b-sum" id="totalDisplay">632</span>
  </div>

  
  <div class="chart-container">
    <svg viewBox="0 0 540 170">
      <defs>
        
        <marker id="arr-blue" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 1 2 L 7 5 L 1 8 z" fill="#0284c7" />
        </marker>
        <marker id="arr-green" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 1 2 L 7 5 L 1 8 z" fill="#16a34a" />
        </marker>
        <marker id="arr-purple" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 1 2 L 7 5 L 1 8 z" fill="#7c3aed" />
        </marker>
        <marker id="line-arrow" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 2 2 L 8 5 L 2 8 z" fill="#94a3b8" />
        </marker>
      </defs>

      
      <line x1="25" y1="120" x2="515" y2="120" stroke="#94a3b8" stroke-width="3" stroke-linecap="round" marker-end="url(#line-arrow)" />

      
      
      <g id="stepGroup1" style="opacity: 1; transition: opacity 0.35s;">
        <path class="jump-arc arc-1" d="M 50 114 Q 162.5 15 273 114" marker-end="url(#arr-blue)" />
        <rect x="135" y="16" width="55" height="24" rx="12" fill="#e0f2fe" stroke="#38bdf8" stroke-width="1" />
        <text class="tag tag-1" x="162.5" y="32">+200</text>
        <circle cx="275" cy="120" r="5" fill="#0284c7" />
        <line x1="275" y1="114" x2="275" y2="126" stroke="#0284c7" stroke-width="3" />
        <text class="milestone-num" x="275" y="146">547</text>
      </g>

      
      
      <g id="stepGroup2" style="opacity: 1; transition: opacity 0.35s;">
        <path class="jump-arc arc-2" d="M 275 114 Q 337.5 45 398 114" marker-end="url(#arr-green)" />
        <rect x="314" y="36" width="47" height="24" rx="12" fill="#dcfce7" stroke="#4ade80" stroke-width="1" />
        <text class="tag tag-2" x="337.5" y="52">+53</text>
        <circle cx="400" cy="120" r="6" fill="#15803d" />
        <line x1="400" y1="112" x2="400" y2="128" stroke="#15803d" stroke-width="3" />
        <text class="milestone-num landmark" x="400" y="146">600</text>
      </g>

      
      
      <g id="stepGroup3" style="opacity: 1; transition: opacity 0.35s;">
        <path class="jump-arc arc-3" d="M 400 114 Q 442.5 62 483 114" marker-end="url(#arr-purple)" />
        <rect x="420" y="48" width="45" height="24" rx="12" fill="#ede9fe" stroke="#a78bfa" stroke-width="1" />
        <text class="tag tag-3" x="442.5" y="64">+32</text>
        <circle cx="485" cy="120" r="5" fill="#7c3aed" />
        <line x1="485" y1="114" x2="485" y2="126" stroke="#7c3aed" stroke-width="3" />
        <text class="milestone-num" x="485" y="146" fill="#7c3aed">632</text>
      </g>

      
      <g id="startGroup">
        <circle cx="50" cy="120" r="5" fill="#1e2945" />
        <line x1="50" y1="114" x2="50" y2="126" stroke="#1e2945" stroke-width="3" />
        <text class="milestone-num" x="50" y="146">347</text>
      </g>
    </svg>
  </div>

  
  <div class="stepper-controls">
    <button class="step-btn" id="btn0" onclick="setStep(0)">Start</button>
    <button class="step-btn" id="btn1" onclick="setStep(1)">+200</button>
    <button class="step-btn" id="btn2" onclick="setStep(2)">+53</button>
    <button class="step-btn" id="btn3" onclick="setStep(3)">+32</button>
    <button class="step-btn active" id="btnAll" onclick="setStep(4)">All Jumps</button>
  </div>

  <script>
    function setStep(step) {
      // Buttons state
      const buttons = [
        document.getElementById('btn0'),
        document.getElementById('btn1'),
        document.getElementById('btn2'),
        document.getElementById('btn3'),
        document.getElementById('btnAll')
      ];
      buttons.forEach((btn, idx) => {
        if (idx === step) {
          btn.classList.add('active');
        } else {
          btn.classList.remove('active');
        }
      });

      const g1 = document.getElementById('stepGroup1');
      const g2 = document.getElementById('stepGroup2');
      const g3 = document.getElementById('stepGroup3');
      const totalDisplay = document.getElementById('totalDisplay');

      if (step === 0) {
        g1.style.opacity = '0';
        g2.style.opacity = '0';
        g3.style.opacity = '0';
        totalDisplay.textContent = '347';
      } else if (step === 1) {
        g1.style.opacity = '1';
        g2.style.opacity = '0';
        g3.style.opacity = '0';
        totalDisplay.textContent = '547';
      } else if (step === 2) {
        g1.style.opacity = '1';
        g2.style.opacity = '1';
        g3.style.opacity = '0';
        totalDisplay.textContent = '600';
      } else if (step === 3 || step === 4) {
        g1.style.opacity = '1';
        g2.style.opacity = '1';
        g3.style.opacity = '1';
        totalDisplay.textContent = '632';
      }
    }

    // Default display: All jumps active
    setStep(4);
  </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>Decomposing Addition Strategy</title>
  <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;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .main-stage {
      width: 100%;
      max-width: 520px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }

    /* Numbers row */
    .numbers-row {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
    }

    .num-card {
      background: #f8fafc;
      border-radius: 10px;
      padding: 8px 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      border: 1px solid #e2e8f0;
    }

    .num-title {
      font-size: 18px;
      font-weight: 700;
      letter-spacing: -0.5px;
    }

    .blue-title { color: #1d4ed8; }
    .teal-title { color: #0f766e; }

    .split-boxes {
      display: flex;
      gap: 6px;
      width: 100%;
      justify-content: center;
    }

    .box {
      flex: 1;
      text-align: center;
      padding: 6px 2px;
      border-radius: 6px;
      font-weight: 700;
      font-size: 15px;
      transition: all 0.3s ease;
    }

    .box-blue {
      background: #eff6ff;
      border: 1px solid #93c5fd;
      color: #1d4ed8;
    }

    .box-teal {
      background: #f0fdfa;
      border: 1px solid #99f6e4;
      color: #0f766e;
    }

    /* Place value columns */
    .pv-columns {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 8px;
    }

    .pv-col {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      gap: 4px;
      transition: all 0.3s ease;
      position: relative;
    }

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

    .arrow-down {
      font-size: 13px;
      color: #94a3b8;
      line-height: 1;
      margin: 2px 0;
    }

    .pv-calc {
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      white-space: nowrap;
    }

    .pv-sum {
      font-size: 17px;
      font-weight: 800;
      color: #0f172a;
      background: #ffffff;
      border-radius: 6px;
      padding: 2px 8px;
      width: 100%;
      border: 1px solid #cbd5e1;
    }

    /* Highlighting active steps */
    .pv-col.active {
      background: #ffffff;
      border-color: #3b82f6;
      box-shadow: 0 4px 12px rgba(59, 130, 246, 0.15);
    }
    .pv-col.active .pv-sum {
      border-color: #3b82f6;
      color: #1d4ed8;
      background: #eff6ff;
    }

    /* Final Result Card */
    .result-card {
      background: #f0fdf4;
      border: 2px solid #22c55e;
      box-shadow: 0 0 16px rgba(34, 197, 94, 0.25);
      border-radius: 10px;
      padding: 10px 14px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      transition: all 0.3s ease;
    }

    .result-equation {
      font-size: 16px;
      font-weight: 700;
      color: #166534;
      display: flex;
      align-items: center;
      gap: 6px;
      flex-wrap: wrap;
    }

    .total-badge {
      background: #16a34a;
      color: #ffffff;
      font-size: 20px;
      font-weight: 800;
      padding: 2px 10px;
      border-radius: 6px;
    }

    /* Interactive Stepper Navigation */
    .controls {
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 8px;
      margin-top: 4px;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 5px 12px;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      transition: all 0.2s ease;
    }

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

    .step-btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }
  </style>
</head>
<body>

  <div class="main-stage">
    
    <div class="numbers-row">
      
      <div class="num-card">
        <div class="num-title blue-title">436</div>
        <div class="split-boxes">
          <div class="box box-blue" id="b400">400</div>
          <div class="box box-blue" id="b30">30</div>
          <div class="box box-blue" id="b6">6</div>
        </div>
      </div>

      
      <div class="num-card">
        <div class="num-title teal-title">251</div>
        <div class="split-boxes">
          <div class="box box-teal" id="b200">200</div>
          <div class="box box-teal" id="b50">50</div>
          <div class="box box-teal" id="b1">1</div>
        </div>
      </div>
    </div>

    
    <div class="pv-columns">
      
      <div class="pv-col" id="col-hundreds">
        <div class="pv-label">Hundreds</div>
        <div class="arrow-down">↓</div>
        <div class="pv-calc">400 + 200</div>
        <div class="pv-sum">= 600</div>
      </div>

      
      <div class="pv-col" id="col-tens">
        <div class="pv-label">Tens</div>
        <div class="arrow-down">↓</div>
        <div class="pv-calc">30 + 50</div>
        <div class="pv-sum">= 80</div>
      </div>

      
      <div class="pv-col" id="col-ones">
        <div class="pv-label">Ones</div>
        <div class="arrow-down">↓</div>
        <div class="pv-calc">6 + 1</div>
        <div class="pv-sum">= 7</div>
      </div>
    </div>

    
    <div class="result-card" id="res-card">
      <div class="result-equation">
        <span>600</span>
        <span>+</span>
        <span>80</span>
        <span>+</span>
        <span>7</span>
        <span>=</span>
      </div>
      <div class="total-badge">687</div>
    </div>

    
    <div class="controls">
      <button class="step-btn active" onclick="setStep(0)">All</button>
      <button class="step-btn" onclick="setStep(1)">Hundreds</button>
      <button class="step-btn" onclick="setStep(2)">Tens</button>
      <button class="step-btn" onclick="setStep(3)">Ones</button>
      <button class="step-btn" onclick="setStep(4)">Total</button>
    </div>
  </div>

  <script>
    const colH = document.getElementById('col-hundreds');
    const colT = document.getElementById('col-tens');
    const colO = document.getElementById('col-ones');
    const resCard = document.getElementById('res-card');
    
    const b400 = document.getElementById('b400');
    const b200 = document.getElementById('b200');
    const b30 = document.getElementById('b30');
    const b50 = document.getElementById('b50');
    const b6 = document.getElementById('b6');
    const b1 = document.getElementById('b1');

    const buttons = document.querySelectorAll('.step-btn');

    function resetHighlights() {
      [colH, colT, colO].forEach(c => c.classList.remove('active'));
      [b400, b200, b30, b50, b6, b1].forEach(b => {
        b.style.opacity = '1';
        b.style.transform = 'none';
      });
      resCard.style.opacity = '1';
      resCard.style.boxShadow = '0 0 16px rgba(34, 197, 94, 0.25)';
    }

    function setStep(step) {
      buttons.forEach((b, i) => b.classList.toggle('active', i === step));
      resetHighlights();

      if (step === 1) { // Hundreds
        colH.classList.add('active');
        b30.style.opacity = '0.35';
        b50.style.opacity = '0.35';
        b6.style.opacity = '0.35';
        b1.style.opacity = '0.35';
        colT.style.opacity = '0.4';
        colO.style.opacity = '0.4';
        resCard.style.opacity = '0.4';
      } else if (step === 2) { // Tens
        colT.classList.add('active');
        b400.style.opacity = '0.35';
        b200.style.opacity = '0.35';
        b6.style.opacity = '0.35';
        b1.style.opacity = '0.35';
        colH.style.opacity = '0.4';
        colO.style.opacity = '0.4';
        resCard.style.opacity = '0.4';
      } else if (step === 3) { // Ones
        colO.classList.add('active');
        b400.style.opacity = '0.35';
        b200.style.opacity = '0.35';
        b30.style.opacity = '0.35';
        b50.style.opacity = '0.35';
        colH.style.opacity = '0.4';
        colT.style.opacity = '0.4';
        resCard.style.opacity = '0.4';
      } else if (step === 4) { // Total
        colH.style.opacity = '0.5';
        colT.style.opacity = '0.5';
        colO.style.opacity = '0.5';
        resCard.style.boxShadow = '0 0 22px rgba(34, 197, 94, 0.45)';
      }
    }
  </script>
</body>
</html>

Understanding Thousands, Hundreds, Tens and Ones

Reading and Writing Four-Digit Numbers

Partitioning Four-Digit Numbers into Standard Parts

Flexible Partitioning of Four-Digit Numbers

Finding 10, 100, and 1,000 More or Less

Counting Forwards and Backwards in Thousands

Counting in Multiples of Twenty-Five

Counting in Multiples of Six and Nine

Counting in Multiples of Seven

Locating 4-Digit Numbers on Number Lines

Representing Four-Digit Numbers with Place Value Counters

Solving Place Value Riddles and Problems Within 10,000

math

Place Value: Four-Digit Numbers and Counting in Multiples

Calcul mental : ajouter ou soustraire des unités à un décimal sans retenue

Calcul mental : ajouter ou soustraire des dizaines et centaines à un décimal

Calcul mental : ajouter ou soustraire des dixièmes et centièmes sans retenue

Multiplier un nombre entier par 10, 100 ou 1 000

Multiplier un nombre décimal par 10

Diviser un nombre décimal par 10

Calcul mental et numération décimale

Ajouter ou soustraire 9 et 19 par compensation

Ajouter ou soustraire 8 et 18 par compensation

Ajouter ou soustraire 28, 29, 38, 39 jusqu'à 98 ou 99

Multiplier un chiffre par un nombre entier de dizaines ou centaines

Multiplier des dizaines, des centaines et des milliers entre elles

Utiliser la distributivité simple pour multiplier mentalement

Utiliser la distributivité avec soustraction : multiplier par 19 ou 29

Diviser un nombre entier par 4 en prenant la moitié de la moitié

Diviser un nombre entier par 8 en prenant trois fois la moitié

Défis et stratégies croisées de calcul mental sur les entiers

Calcul mental sur les entiers : compensations, distributivité et ordres de grandeur

OGM.5.NBT.3

Aligned learning resources

Related diagrams