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

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      min-height: 100%;
    }

    .callout {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: #eff6ff;
      border: 1.5px solid #bfdbfe;
      color: #1d4ed8;
      font-size: 15px;
      font-weight: 700;
      padding: 6px 14px;
      border-radius: 999px;
      margin-bottom: 14px;
    }

    .comparison {
      display: flex;
      flex-direction: row;
      gap: 16px;
      width: 100%;
      max-width: 480px;
      justify-content: center;
    }

    .panel {
      flex: 1;
      display: flex;
      flex-direction: column;
      align-items: center;
      background: #ffffff;
      border-radius: 12px;
      padding: 12px 10px;
      box-shadow: 0 1px 3px rgba(0,0,0,0.06);
    }

    .panel-correct {
      border: 2px solid #86efac;
      background: #f0fdf4;
    }

    .panel-incorrect {
      border: 2px solid #fca5a5;
      background: #fef2f2;
    }

    .badge {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      font-size: 14px;
      font-weight: 800;
      padding: 4px 10px;
      border-radius: 6px;
      margin-bottom: 10px;
    }

    .badge-correct {
      background: #dcfce7;
      color: #15803d;
    }

    .badge-incorrect {
      background: #fee2e2;
      color: #b91c1c;
    }

    /* Math Grid */
    .math-grid {
      display: grid;
      grid-template-columns: 20px 32px 32px 32px;
      row-gap: 2px;
      font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
      font-size: 20px;
      font-weight: 700;
      text-align: center;
      align-items: center;
    }

    .header-cell {
      font-family: system-ui, sans-serif;
      font-size: 12px;
      font-weight: 800;
      color: #64748b;
      padding-bottom: 4px;
    }

    .cell {
      height: 32px;
      display: flex;
      align-items: center;
      justify-content: center;
      border-radius: 4px;
    }

    .op {
      font-family: system-ui, sans-serif;
      color: #64748b;
      font-weight: 600;
    }

    .ones-col {
      background: rgba(59, 130, 246, 0.12);
      color: #1d4ed8;
    }

    .empty-cell {
      color: #cbd5e1;
    }

    .divider {
      grid-column: 1 / -1;
      height: 2px;
      background: #334155;
      margin: 2px 0 4px 0;
    }

    .sum-row {
      font-size: 21px;
    }

    .sum-correct {
      color: #15803d;
    }

    .sum-incorrect {
      color: #b91c1c;
      text-decoration: line-through;
      text-decoration-thickness: 2px;
    }

    .col-line {
      border-right: 1px dashed rgba(100, 116, 139, 0.25);
    }

    @media (max-width: 380px) {
      .comparison {
        gap: 8px;
      }
      .math-grid {
        grid-template-columns: 16px 28px 28px 28px;
        font-size: 18px;
      }
      .cell {
        height: 28px;
      }
      .callout {
        font-size: 13px;
        padding: 4px 10px;
      }
    }
  </style>
</head>
<body>

  <div class="callout">
    <span>✦</span> Always align the ones!
  </div>

  <div class="comparison">
    
    <div class="panel panel-correct">
      <div class="badge badge-correct">✓ Correct</div>
      
      <div class="math-grid">
        <div></div>
        <div class="header-cell col-line">H</div>
        <div class="header-cell col-line">T</div>
        <div class="header-cell ones-col">O</div>

        <div></div>
        <div class="cell col-line">5</div>
        <div class="cell col-line">4</div>
        <div class="cell ones-col">1</div>

        <div class="cell op">+</div>
        <div class="cell empty-cell col-line">·</div>
        <div class="cell col-line">3</div>
        <div class="cell ones-col">7</div>

        <div class="divider"></div>

        <div></div>
        <div class="cell col-line sum-row sum-correct">5</div>
        <div class="cell col-line sum-row sum-correct">7</div>
        <div class="cell ones-col sum-row sum-correct">8</div>
      </div>
    </div>

    
    <div class="panel panel-incorrect">
      <div class="badge badge-incorrect">✗ Incorrect</div>
      
      <div class="math-grid">
        <div></div>
        <div class="header-cell col-line">H</div>
        <div class="header-cell col-line">T</div>
        <div class="header-cell">O</div>

        <div></div>
        <div class="cell col-line">5</div>
        <div class="cell col-line">4</div>
        <div class="cell">1</div>

        <div class="cell op">+</div>
        <div class="cell col-line">3</div>
        <div class="cell col-line">7</div>
        <div class="cell empty-cell">·</div>

        <div class="divider"></div>

        <div></div>
        <div class="cell col-line sum-row sum-incorrect">9</div>
        <div class="cell col-line sum-row sum-incorrect">1</div>
        <div class="cell sum-row sum-incorrect">1</div>
      </div>
    </div>
  </div>

</body>
</html>

Adding Three-Digit Numbers Without Regrouping

<!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;
      padding: 16px;
      min-height: 100%;
      user-select: none;
    }
    .diagram-area {
      width: 100%;
      max-width: 460px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
      margin: auto 0;
    }
    /* Top problem */
    .top-problem {
      font-size: 28px;
      font-weight: 800;
      letter-spacing: 0.5px;
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .num-base { color: #1e2945; }
    .num-split {
      color: #2563eb;
      position: relative;
      display: inline-block;
      padding: 2px 8px;
      background: #eff6ff;
      border-radius: 8px;
      border: 1.5px dashed #93c5fd;
    }

    /* Branch SVG */
    .branch-container {
      width: 180px;
      height: 42px;
      position: relative;
    }
    .branch-svg {
      width: 100%;
      height: 100%;
    }

    /* Split branches pills */
    .branches-row {
      display: flex;
      justify-content: center;
      gap: 36px;
      margin-top: -6px;
    }
    .pill {
      font-size: 16px;
      font-weight: 700;
      padding: 4px 12px;
      border-radius: 20px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      transition: all 0.3s ease;
    }
    .pill-blue {
      background: #dbeafe;
      color: #1d4ed8;
      border: 1.5px solid #93c5fd;
    }
    .pill-purple {
      background: #f3e8ff;
      color: #7e22ce;
      border: 1.5px solid #d8b4fe;
    }

    /* Steps container */
    .steps-list {
      width: 100%;
      display: flex;
      flex-direction: column;
      gap: 10px;
      margin-top: 6px;
    }
    .step-card {
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 14px;
      padding: 10px 14px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      transition: all 0.3s ease;
      opacity: 0.35;
      transform: scale(0.98);
    }
    .step-card.active {
      opacity: 1;
      transform: scale(1);
      background: #ffffff;
      border-color: #3b82f6;
      box-shadow: 0 4px 12px rgba(59, 130, 246, 0.12);
    }
    .step-card.step-2.active {
      border-color: #10b981;
      box-shadow: 0 4px 12px rgba(16, 185, 129, 0.12);
    }

    .step-left {
      display: flex;
      align-items: center;
      gap: 10px;
    }
    .step-tag {
      font-size: 11px;
      font-weight: 800;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      padding: 3px 7px;
      border-radius: 6px;
      background: #e2e8f0;
      color: #475569;
    }
    .step-card.active .step-tag {
      background: #dbeafe;
      color: #1d4ed8;
    }
    .step-card.step-2.active .step-tag {
      background: #d1fae5;
      color: #047857;
    }

    .step-math {
      font-size: 19px;
      font-weight: 700;
      color: #1e2945;
    }
    .highlight-blue {
      color: #1d4ed8;
      font-weight: 800;
    }
    .highlight-purple {
      color: #7e22ce;
      font-weight: 800;
    }
    .highlight-tens {
      color: #0284c7;
      background: #e0f2fe;
      padding: 1px 6px;
      border-radius: 6px;
    }

    .step-badge {
      font-size: 13px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 20px;
      display: flex;
      align-items: center;
      gap: 4px;
      white-space: nowrap;
    }
    .badge-tens {
      background: #e0f2fe;
      color: #0369a1;
    }
    .badge-done {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #86efac;
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      gap: 12px;
      margin-top: 10px;
    }
    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 14px;
      border-radius: 8px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background 0.2s;
    }
    .btn:hover {
      background: #e2e8f0;
    }
    .dots {
      display: flex;
      gap: 6px;
    }
    .dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .dot.active {
      background: #2563eb;
      transform: scale(1.2);
    }
  </style>
</head>
<body>

  <div class="diagram-area">
    
    <div class="top-problem">
      <span class="num-base">476 +</span>
      <span class="num-split">8</span>
    </div>

    
    <div class="branch-container">
      <svg class="branch-svg" viewBox="0 0 180 42">
        
        <path d="M 90 2 Q 90 24, 40 40" fill="none" stroke="#3b82f6" stroke-width="2.5" stroke-linecap="round" />
        
        <path d="M 90 2 Q 90 24, 140 40" fill="none" stroke="#a855f7" stroke-width="2.5" stroke-linecap="round" />
      </svg>
    </div>

    
    <div class="branches-row">
      <div class="pill pill-blue">+4</div>
      <div class="pill pill-purple">+4</div>
    </div>

    
    <div class="steps-list">
      
      <div id="stepCard1" class="step-card active">
        <div class="step-left">
          <span class="step-tag">Step 1</span>
          <span class="step-math">476 + <span class="highlight-blue">4</span> = <span class="highlight-tens">480</span></span>
        </div>
        <div class="step-badge badge-tens">🎯 Next Ten</div>
      </div>

      
      <div id="stepCard2" class="step-card step-2 active">
        <div class="step-left">
          <span class="step-tag">Step 2</span>
          <span class="step-math">480 + <span class="highlight-purple">4</span> = <strong>484</strong></span>
        </div>
        <div class="step-badge badge-done">✓ 484</div>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button id="btnPrev" class="btn" onclick="setStep(currStep - 1)">◀</button>
    <div class="dots">
      <span class="dot" onclick="setStep(0)"></span>
      <span class="dot" onclick="setStep(1)"></span>
      <span class="dot active" onclick="setStep(2)"></span>
    </div>
    <button id="btnNext" class="btn" onclick="setStep(currStep + 1)">▶</button>
  </div>

  <script>
    let currStep = 2; // 0 = split only, 1 = step 1 focus, 2 = all complete

    const card1 = document.getElementById('stepCard1');
    const card2 = document.getElementById('stepCard2');
    const dots = document.querySelectorAll('.dot');

    function setStep(idx) {
      if (idx < 0) idx = 0;
      if (idx > 2) idx = 2;
      currStep = idx;

      // Update cards
      if (currStep === 0) {
        card1.classList.remove('active');
        card2.classList.remove('active');
      } else if (currStep === 1) {
        card1.classList.add('active');
        card2.classList.remove('active');
      } else {
        card1.classList.add('active');
        card2.classList.add('active');
      }

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

    setStep(2);
  </script>
</body>
</html>

Adding and Subtracting Ones Mentally Crossing Tens

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

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

    .expression {
      font-size: 26px;
      font-weight: 800;
      letter-spacing: -0.5px;
      color: #1e2945;
    }

    .expression .split-num {
      color: #d97706;
      border-bottom: 2px dashed #f59e0b;
      padding-bottom: 1px;
    }

    .svg-container {
      width: 100%;
      max-width: 580px;
      margin: 4px 0;
    }

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

    .jump-path {
      fill: none;
      stroke-width: 3.5;
      stroke-linecap: round;
      stroke-linejoin: round;
      transition: stroke-dashoffset 0.6s ease, opacity 0.4s ease;
    }

    .jump-orange {
      stroke: #f59e0b;
    }

    .jump-red {
      stroke: #ef4444;
    }

    .jump-label {
      font-size: 15px;
      font-weight: 700;
      text-anchor: middle;
      transition: opacity 0.3s ease, transform 0.3s ease;
    }

    .tick-label {
      font-size: 13px;
      font-weight: 600;
      fill: #6b7280;
      text-anchor: middle;
      font-family: inherit;
    }

    .tick-label.key {
      font-size: 14px;
      font-weight: 800;
      fill: #1e2945;
    }

    .tick-label.highlight-start {
      fill: #d97706;
    }

    .tick-label.highlight-ten {
      fill: #0284c7;
    }

    .tick-label.highlight-end {
      fill: #16a34a;
    }

    .steps-card {
      display: flex;
      flex-wrap: wrap;
      gap: 8px;
      justify-content: center;
      width: 100%;
      max-width: 540px;
      margin-top: 4px;
    }

    .step-box {
      flex: 1;
      min-width: 210px;
      background: #f8fafc;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 14px;
      display: flex;
      align-items: center;
      gap: 10px;
      transition: all 0.3s ease;
    }

    .step-box.active {
      border-color: #cbd5e1;
      box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
    }

    .step-box.step1.active {
      border-color: #f59e0b;
      background: #fffbeb;
    }

    .step-box.step2.active {
      border-color: #ef4444;
      background: #fef2f2;
    }

    .step-tag {
      font-size: 11px;
      font-weight: 800;
      text-transform: uppercase;
      padding: 3px 7px;
      border-radius: 6px;
      letter-spacing: 0.5px;
    }

    .step1 .step-tag {
      background: #fef3c7;
      color: #b45309;
    }

    .step2 .step-tag {
      background: #fee2e2;
      color: #b91c1c;
    }

    .step-math {
      font-size: 16px;
      font-weight: 700;
      color: #1e2945;
      font-variant-numeric: tabular-nums;
    }

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

    .btn {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      border-radius: 8px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 700;
      color: #334155;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 5px;
      user-select: none;
      transition: background 0.15s, border-color 0.15s;
    }

    .btn:active {
      background: #e2e8f0;
    }

    .btn.active-tab {
      background: #2563eb;
      border-color: #2563eb;
      color: #ffffff;
    }
  </style>
</head>
<body>

  <div class="header">
    <div class="expression">532 − <span class="split-num">7</span> = <strong>525</strong></div>
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 560 160" preserveAspectRatio="xMidYMid meet">
      <defs>
        
        <marker id="arrow-orange" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 10 2 L 2 5 L 10 8 z" fill="#f59e0b" />
        </marker>
        
        <marker id="arrow-red" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 10 2 L 2 5 L 10 8 z" fill="#ef4444" />
        </marker>
      </defs>

      
      <line x1="30" y1="120" x2="530" y2="120" stroke="#cbd5e1" stroke-width="3" stroke-linecap="round" />

      
      
      
      <g stroke="#94a3b8" stroke-width="2" stroke-linecap="round">
        <line x1="72" y1="115" x2="72" y2="125" />
        <line x1="104" y1="115" x2="104" y2="125" />
        <line x1="136" y1="115" x2="136" y2="125" />
        <line x1="168" y1="115" x2="168" y2="125" />
        <line x1="232" y1="115" x2="232" y2="125" />
        <line x1="264" y1="115" x2="264" y2="125" />
        <line x1="296" y1="115" x2="296" y2="125" />
        <line x1="328" y1="115" x2="328" y2="125" />
        <line x1="392" y1="115" x2="392" y2="125" />
        <line x1="456" y1="115" x2="456" y2="125" />
        <line x1="488" y1="115" x2="488" y2="125" />
      </g>

      
      <g stroke="#475569" stroke-width="2.5" stroke-linecap="round">
        <line x1="40" y1="112" x2="40" y2="128" />
        <line x1="200" y1="110" x2="200" y2="130" stroke="#16a34a" stroke-width="3" />
        <line x1="360" y1="110" x2="360" y2="130" stroke="#0284c7" stroke-width="3" />
        <line x1="424" y1="110" x2="424" y2="130" stroke="#d97706" stroke-width="3" />
        <line x1="520" y1="112" x2="520" y2="128" />
      </g>

      
      <text x="40" y="148" class="tick-label">520</text>
      <text x="200" y="148" class="tick-label key highlight-end">525</text>
      <text x="360" y="148" class="tick-label key highlight-ten">530</text>
      <text x="424" y="148" class="tick-label key highlight-start">532</text>
      <text x="520" y="148" class="tick-label">535</text>

      
      <circle cx="424" cy="120" r="5" fill="#f59e0b" />
      <circle cx="360" cy="120" r="5" fill="#0284c7" />
      <circle cx="200" cy="120" r="5" fill="#16a34a" />

      
      
      <g id="jump1Group">
        <path id="jump1" class="jump-path jump-orange" d="M 424 114 C 420 55, 368 55, 364 114" marker-end="url(#arrow-orange)" />
        <rect x="376" y="32" width="36" height="24" rx="12" fill="#fffbeb" stroke="#f59e0b" stroke-width="1.5" />
        <text x="394" y="49" class="jump-label" fill="#b45309">−2</text>
      </g>

      
      
      <g id="jump2Group">
        <path id="jump2" class="jump-path jump-red" d="M 360 114 C 350 25, 212 25, 204 114" marker-end="url(#arrow-red)" />
        <rect x="264" y="12" width="36" height="24" rx="12" fill="#fef2f2" stroke="#ef4444" stroke-width="1.5" />
        <text x="282" y="29" class="jump-label" fill="#b91c1c">−5</text>
      </g>
    </svg>
  </div>

  <div class="steps-card">
    <div class="step-box step1 active" id="cardStep1">
      <span class="step-tag">Step 1</span>
      <span class="step-math">532 − 2 = <strong>530</strong></span>
    </div>
    <div class="step-box step2 active" id="cardStep2">
      <span class="step-tag">Step 2</span>
      <span class="step-math">530 − 5 = <strong>525</strong></span>
    </div>
  </div>

  <div class="controls">
    <button class="btn" id="btnStep1">1. Take 2 to 530</button>
    <button class="btn" id="btnStep2">2. Take 5 to 525</button>
    <button class="btn active-tab" id="btnAll">Show All</button>
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</html>

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<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
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  <title>Near-Ten Compensation Strategy</title>
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</head>
<body>

  <div class="header">
    <div class="title">Near-Ten Compensation Strategy (+9 and −9)</div>
    <div class="subtitle">Jump to the nearest ten, then compensate by 1</div>
  </div>

  <div class="grid">
    
    <div class="column">
      <div class="col-title col-title-add">
        <span>+9 Strategy: 456 + 9</span>
      </div>

      <div class="svg-container">
        <svg viewBox="0 0 320 135">
          <defs>
            <marker id="arr-blue" viewBox="0 0 8 8" refX="6" refY="4" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
              <path d="M 1 1 L 7 4 L 1 7 z" fill="#0284c7" />
            </marker>
            <marker id="arr-rose" viewBox="0 0 8 8" refX="6" refY="4" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
              <path d="M 1 1 L 7 4 L 1 7 z" fill="#e11d48" />
            </marker>
          </defs>

          
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          <line x1="45" y1="94" x2="45" y2="106" class="tick" />
          <line x1="215" y1="94" x2="215" y2="106" class="tick" />
          <line x1="275" y1="94" x2="275" y2="106" class="tick" />

          
          
          <g id="add-step1" class="anim-el">
            <path d="M 45 92 C 110 20, 210 20, 273 92" class="arc-add-10" marker-end="url(#arr-blue)" />
            <rect x="135" y="24" width="48" height="20" rx="10" fill="#e0f2fe" />
            <text x="159" y="38" class="arc-label" fill="#0284c7">+10</text>
          </g>

          
          <g id="add-step2" class="anim-el">
            <path d="M 275 92 C 265 60, 225 60, 217 92" class="arc-sub-1" marker-end="url(#arr-rose)" />
            <rect x="230" y="52" width="30" height="18" rx="9" fill="#ffe4e6" />
            <text x="245" y="65" class="arc-label" fill="#e11d48" font-size="11">−1</text>
          </g>

          
          
          <circle cx="45" cy="100" r="4.5" fill="#475569" />
          <text x="45" y="120" class="num-label">456</text>

          
          <circle cx="275" cy="100" r="4.5" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="2,2" />
          <text x="275" y="120" class="num-label" fill="#94a3b8">466</text>

          
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          <rect x="195" y="110" width="40" height="18" rx="4" fill="#0284c7" />
          <text x="215" y="123" class="num-highlight" fill="#ffffff">465</text>
        </svg>
      </div>

      <div class="formula-box">
        456 + 9 = 456 <span class="c-blue">+ 10</span> <span class="c-rose">− 1</span> = <span class="c-target">465</span>
      </div>
    </div>

    
    <div class="column">
      <div class="col-title col-title-sub">
        <span>−9 Strategy: 456 − 9</span>
      </div>

      <div class="svg-container">
        <svg viewBox="0 0 320 135">
          <defs>
            <marker id="arr-amber" viewBox="0 0 8 8" refX="6" refY="4" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
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          <line x1="275" y1="94" x2="275" y2="106" class="tick" />

          
          
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            <path d="M 275 92 C 210 20, 110 20, 47 92" class="arc-sub-10" marker-end="url(#arr-amber)" />
            <rect x="135" y="24" width="48" height="20" rx="10" fill="#fef3c7" />
            <text x="159" y="38" class="arc-label" fill="#d97706">−10</text>
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            <path d="M 45 92 C 55 60, 95 60, 103 92" class="arc-add-1" marker-end="url(#arr-emerald)" />
            <rect x="60" y="52" width="30" height="18" rx="9" fill="#d1fae5" />
            <text x="75" y="65" class="arc-label" fill="#059669" font-size="11">+1</text>
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          <text x="45" y="120" class="num-label" fill="#94a3b8">446</text>

          
          <circle cx="105" cy="100" r="6" fill="#d97706" />
          <rect x="85" y="110" width="40" height="18" rx="4" fill="#d97706" />
          <text x="105" y="123" class="num-highlight" fill="#ffffff">447</text>

          
          <circle cx="275" cy="100" r="4.5" fill="#475569" />
          <text x="275" y="120" class="num-label">456</text>
        </svg>
      </div>

      <div class="formula-box">
        456 − 9 = 456 <span class="c-amber">− 10</span> <span class="c-emerald">+ 1</span> = <span class="c-target">447</span>
      </div>
    </div>
  </div>

  
  <div class="step-btn-group">
    <button class="step-btn active" id="btn-all" onclick="showStep('all')">Show Both Steps</button>
    <button class="step-btn" id="btn-step1" onclick="showStep('1')">Step 1: Jump 10</button>
    <button class="step-btn" id="btn-step2" onclick="showStep('2')">Step 2: Adjust 1</button>
  </div>

  
  <div class="summary-strip">
    <div class="rule-pill rule-add">
      <span>✦ <b>To Add 9:</b> Jump <b>+10</b>, then <b>−1</b></span>
    </div>
    <div class="rule-pill rule-sub">
      <span>✦ <b>To Subtract 9:</b> Jump <b>−10</b>, then <b>+1</b></span>
    </div>
  </div>

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</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>Decomposition Method: 643 - 8</title>
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      gap: 4px;
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</head>
<body>

  
  <div class="stepper-nav">
    <button class="step-btn active" id="btn0" onclick="goToStep(0)">1. Split 643</button>
    <button class="step-btn" id="btn1" onclick="goToStep(1)">2. Subtract 10 − 8</button>
    <button class="step-btn" id="btn2" onclick="goToStep(2)">3. Add Back</button>
    <button class="play-btn" id="playBtn" onclick="togglePlay()">⏸ Pause</button>
  </div>

  
  <div class="diagram-area">
    
    <div class="problem-row">
      <div class="num-pill num-main" id="topNum">643</div>
      <div class="op">−</div>
      <div class="num-pill num-sub" id="topSub">8</div>
    </div>

    
    <div class="bond-tree">
      <svg class="svg-lines" viewBox="0 0 380 40">
        
        <line x1="190" y1="0" x2="85" y2="38" stroke="#0284c7" stroke-width="2.5" stroke-linecap="round" />
        <line x1="190" y1="0" x2="295" y2="38" stroke="#0284c7" stroke-width="2.5" stroke-linecap="round" />
      </svg>

      <div class="split-row">
        
        <div class="bond-left">
          <div class="num-pill num-base" id="pill630">630</div>
        </div>

        
        <div class="bond-right">
          <div class="num-group">
            <div class="num-pill num-thirteen" id="pill13">13</div>
            
            <svg class="mini-svg" viewBox="0 0 110 28">
              <line x1="55" y1="0" x2="25" y2="26" stroke="#d97706" stroke-width="2" stroke-linecap="round" />
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            <div class="mini-split">
              <div class="num-pill num-ten" id="pill10">10</div>
              <div class="num-pill num-three" id="pill3">3</div>
            </div>
          </div>
        </div>
      </div>
    </div>

    
    <div class="work-card" id="workCard">
      <span>Subtract:</span>
      <span class="num-pill num-ten" style="font-size:15px; padding:2px 8px;">10</span>
      <span>−</span>
      <span class="num-pill num-sub" style="font-size:15px; padding:2px 8px;">8</span>
      <span>=</span>
      <span class="diff-badge">2</span>
    </div>

    
    <div class="summary-bubble" id="summaryCard">
      <span>630</span>
      <span>+</span>
      <span>2</span>
      <span>+</span>
      <span>3</span>
      <span>=</span>
      <span class="final-ans">635</span>
    </div>
  </div>

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

    const workCard = document.getElementById('workCard');
    const summaryCard = document.getElementById('summaryCard');
    const pill630 = document.getElementById('pill630');
    const pill10 = document.getElementById('pill10');
    const pill3 = document.getElementById('pill3');
    const pill13 = document.getElementById('pill13');
    const playBtn = document.getElementById('playBtn');

    function updateView() {
      for (let i = 0; i < 3; i++) {
        const btn = document.getElementById('btn' + i);
        if (btn) btn.classList.toggle('active', i === currentStep);
      }

      if (currentStep === 0) {
        // Step 1: Just show decomposition
        workCard.classList.add('dimmed');
        workCard.classList.remove('active-card');
        summaryCard.classList.add('dimmed');

        pill630.classList.remove('dimmed');
        pill13.classList.remove('dimmed');
        pill10.classList.remove('dimmed');
        pill3.classList.remove('dimmed');
      } else if (currentStep === 1) {
        // Step 2: Highlight 10 - 8
        workCard.classList.remove('dimmed');
        workCard.classList.add('active-card');
        summaryCard.classList.add('dimmed');

        pill630.classList.add('dimmed');
        pill13.classList.add('dimmed');
        pill10.classList.remove('dimmed');
        pill3.classList.add('dimmed');
      } else {
        // Step 3: Combine all in summary
        workCard.classList.remove('active-card');
        workCard.classList.remove('dimmed');
        summaryCard.classList.remove('dimmed');

        pill630.classList.remove('dimmed');
        pill13.classList.add('dimmed');
        pill10.classList.remove('dimmed');
        pill3.classList.remove('dimmed');
      }
    }

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

    function nextStep() {
      currentStep = (currentStep + 1) % 3;
      updateView();
    }

    function startTimer() {
      stopTimer();
      timer = setInterval(nextStep, 3500);
    }

    function stopTimer() {
      if (timer) {
        clearInterval(timer);
        timer = null;
      }
    }

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

    // Initialize
    updateView();
    startTimer();
  </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;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      background: #ffffff;
      color: #0f172a;
      padding: 12px 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      max-width: 680px;
      margin: 0 auto;
    }

    .panels {
      display: flex;
      flex-direction: row;
      gap: 12px;
      width: 100%;
    }

    @media (max-width: 480px) {
      .panels {
        flex-direction: column;
        gap: 10px;
      }
    }

    .side-card {
      flex: 1;
      background: #f8fafc;
      border: 1px solid #cbd5e1;
      border-radius: 12px;
      padding: 12px 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
    }

    .side-title {
      font-size: 13px;
      font-weight: 800;
      text-transform: uppercase;
      letter-spacing: 0.6px;
      margin-bottom: 6px;
    }

    .add-title { color: #0369a1; }
    .sub-title { color: #c2410c; }

    .math-row {
      font-size: 26px;
      font-weight: 800;
      margin-bottom: 4px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
    }

    .tree-box {
      position: relative;
      width: 140px;
      height: 60px;
      margin-bottom: 6px;
    }

    .tree-svg {
      width: 100%;
      height: 100%;
      overflow: visible;
    }

    .line-branch {
      stroke-dasharray: 45;
      stroke-dashoffset: 45;
      transition: stroke-dashoffset 0.35s ease-out;
    }

    .line-branch.active {
      stroke-dashoffset: 0;
    }

    .tree-num {
      position: absolute;
      font-size: 14px;
      font-weight: 800;
      width: 32px;
      height: 30px;
      display: flex;
      align-items: center;
      justify-content: center;
      border-radius: 6px;
      transition: all 0.3s ease;
      opacity: 0.15;
      transform: translateY(-3px);
    }

    .tree-num.active {
      opacity: 1;
      transform: translateY(0);
    }

    .add-left { top: 28px; left: 14px; background: #e0f2fe; color: #075985; border: 1.5px solid #38bdf8; }
    .add-right { top: 28px; right: 14px; background: #e0f2fe; color: #075985; border: 1.5px solid #38bdf8; }
    .sub-left { top: 28px; left: 14px; background: #ffedd5; color: #9a3412; border: 1.5px solid #fb923c; }
    .sub-right { top: 28px; right: 14px; background: #ffedd5; color: #9a3412; border: 1.5px solid #fb923c; }

    .step-explain {
      font-size: 12px;
      font-weight: 600;
      color: #475569;
      min-height: 28px;
      display: flex;
      align-items: center;
      justify-content: center;
      padding: 0 4px;
      margin-bottom: 6px;
    }

    .flow-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      min-height: 44px;
    }

    .badge {
      font-size: 16px;
      font-weight: 800;
      padding: 5px 12px;
      border-radius: 8px;
      transition: all 0.3s ease;
      opacity: 0.18;
      transform: scale(0.96);
    }

    .badge.active {
      opacity: 1;
      transform: scale(1);
    }

    /* High contrast transition badges */
    .badge-hundred-add {
      background: #0369a1;
      color: #ffffff;
      border: 1px solid #075985;
      box-shadow: 0 2px 4px rgba(3, 105, 161, 0.2);
    }

    .badge-hundred-sub {
      background: #c2410c;
      color: #ffffff;
      border: 1px solid #9a3412;
      box-shadow: 0 2px 4px rgba(194, 65, 12, 0.2);
    }

    .badge-final-add {
      background: #0f766e;
      color: #ffffff;
      border: 1px solid #115e59;
      box-shadow: 0 2px 4px rgba(15, 118, 110, 0.2);
    }

    .badge-final-sub {
      background: #4338ca;
      color: #ffffff;
      border: 1px solid #3730a3;
      box-shadow: 0 2px 4px rgba(67, 56, 202, 0.2);
    }

    .arrow-sym {
      font-size: 18px;
      font-weight: 900;
      color: #94a3b8;
      opacity: 0.2;
      transition: all 0.3s ease;
    }

    .arrow-sym.active {
      opacity: 1;
      color: #1e293b;
    }

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

    .btn-step {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      border-radius: 8px;
      padding: 6px 10px;
      font-size: 12px;
      font-weight: 700;
      color: #334155;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
      transition: background-color 0.2s, border-color 0.2s, color 0.2s;
    }

    .btn-step.active {
      background: #1e293b;
      border-color: #1e293b;
      color: #ffffff;
    }

    .play-btn {
      background: #f8fafc;
      border: 1.5px solid #cbd5e1;
      border-radius: 8px;
      width: 32px;
      height: 30px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 13px;
      cursor: pointer;
      color: #0f172a;
      font-weight: bold;
      transition: background-color 0.2s, border-color 0.2s;
    }
  </style>
</head>
<body>

  <div class="panels">
    
    <div class="side-card">
      <div class="side-title add-title">Addition Across Hundreds</div>
      <div class="math-row">
        <span>297</span>
        <span style="color:#0284c7;">+</span>
        <span style="color:#0284c7;">5</span>
      </div>

      <div class="tree-box">
        <svg class="tree-svg" viewBox="0 0 140 60" aria-hidden="true">
          <path id="addBranchL" class="line-branch" d="M 70,2 L 30,28" stroke="#0284c7" stroke-width="2.5" fill="none" stroke-linecap="round"/>
          <path id="addBranchR" class="line-branch" d="M 70,2 L 110,28" stroke="#0284c7" stroke-width="2.5" fill="none" stroke-linecap="round"/>
        </svg>
        <div id="addNumL" class="tree-num add-left">+3</div>
        <div id="addNumR" class="tree-num add-right">+2</div>
      </div>

      <div id="addExp" class="step-explain">Add 3 to hit 300, then add 2 more</div>

      <div class="flow-row">
        <div id="addH" class="badge badge-hundred-add">300</div>
        <div id="addArr" class="arrow-sym">→</div>
        <div id="addFin" class="badge badge-final-add">302</div>
      </div>
    </div>

    
    <div class="side-card">
      <div class="side-title sub-title">Subtraction Across Hundreds</div>
      <div class="math-row">
        <span>403</span>
        <span style="color:#ea580c;">−</span>
        <span style="color:#ea580c;">6</span>
      </div>

      <div class="tree-box">
        <svg class="tree-svg" viewBox="0 0 140 60" aria-hidden="true">
          <path id="subBranchL" class="line-branch" d="M 70,2 L 30,28" stroke="#ea580c" stroke-width="2.5" fill="none" stroke-linecap="round"/>
          <path id="subBranchR" class="line-branch" d="M 70,2 L 110,28" stroke="#ea580c" stroke-width="2.5" fill="none" stroke-linecap="round"/>
        </svg>
        <div id="subNumL" class="tree-num sub-left">−3</div>
        <div id="subNumR" class="tree-num sub-right">−3</div>
      </div>

      <div id="subExp" class="step-explain">Subtract 3 to hit 400, then drop into 390s</div>

      <div class="flow-row">
        <div id="subH" class="badge badge-hundred-sub">400</div>
        <div id="subArr" class="arrow-sym">→</div>
        <div id="subFin" class="badge badge-final-sub">397</div>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button class="btn-step active" onclick="setStep(0)">1. Problem</button>
    <button class="btn-step" onclick="setStep(1)">2. Split</button>
    <button class="btn-step" onclick="setStep(2)">3. Bridge Hundred</button>
    <button class="btn-step" onclick="setStep(3)">4. Result</button>
    <button id="playBtn" class="play-btn" onclick="togglePlay()" aria-label="Play/Pause">⏸</button>
  </div>

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

    const descriptions = [
      { add: "Original problem: 297 + 5", sub: "Original problem: 403 − 6" },
      { add: "Split 5 into +3 (reach 300) and +2", sub: "Split 6 into −3 (reach 400) and −3" },
      { add: "297 + 3 reaches 300 benchmark", sub: "403 − 3 reaches 400 benchmark" },
      { add: "300 + 2 completes the sum: 302", sub: "400 − 3 drops into the 390s: 397" }
    ];

    const steps = [
      () => toggleClasses(false, false, false),
      () => toggleClasses(true, false, false),
      () => toggleClasses(true, true, false),
      () => toggleClasses(true, true, true)
    ];

    function toggleClasses(split, hundred, final) {
      ['addBranchL', 'addBranchR', 'subBranchL', 'subBranchR', 'addNumL', 'addNumR', 'subNumL', 'subNumR'].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.classList.toggle('active', split);
      });

      ['addH', 'subH'].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.classList.toggle('active', hundred);
      });

      ['addArr', 'subArr', 'addFin', 'subFin'].forEach(id => {
        const el = document.getElementById(id);
        if (el) el.classList.toggle('active', final);
      });

      document.getElementById('addExp').textContent = descriptions[currentStep].add;
      document.getElementById('subExp').textContent = descriptions[currentStep].sub;
    }

    function setStep(index) {
      currentStep = index;
      document.querySelectorAll('.btn-step').forEach((btn, i) => {
        btn.classList.toggle('active', i === currentStep);
      });
      steps[currentStep]();
    }

    function nextStep() {
      setStep((currentStep + 1) % steps.length);
    }

    function startTimer() {
      clearInterval(timer);
      timer = setInterval(nextStep, 3000);
    }

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

    setStep(0);
    startTimer();
  </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: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      user-select: none;
    }

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

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

    /* Number Line SVG Area */
    .svg-container {
      width: 100%;
      position: relative;
    }

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

    /* Split breakdown box */
    .split-card {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 20px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 16px;
      padding: 12px 24px;
      width: 100%;
      max-width: 480px;
    }

    .split-tree {
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .powerup-bubble {
      background: #f59e0b;
      color: #fff;
      font-weight: 800;
      font-size: 17px;
      width: 36px;
      height: 36px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      box-shadow: 0 2px 6px rgba(245, 158, 11, 0.35);
      z-index: 2;
    }

    .branches {
      display: flex;
      gap: 18px;
      margin-top: 6px;
      position: relative;
    }

    .branch-pill {
      font-size: 15px;
      font-weight: 800;
      padding: 4px 12px;
      border-radius: 20px;
      transition: all 0.3s ease;
    }

    .branch-2 {
      background: #e0f2fe;
      color: #0284c7;
      border: 1.5px solid #0284c7;
    }

    .branch-3 {
      background: #dcfce7;
      color: #16a34a;
      border: 1.5px solid #16a34a;
    }

    .math-steps {
      display: flex;
      flex-direction: column;
      gap: 6px;
      font-size: 16px;
      font-weight: 700;
      font-family: ui-monospace, monospace;
    }

    .math-row {
      display: flex;
      align-items: center;
      gap: 8px;
      opacity: 0.35;
      transition: opacity 0.3s ease;
    }

    .math-row.active {
      opacity: 1;
    }

    .tag-blue { color: #0284c7; }
    .tag-gold { color: #d97706; background: #fef3c7; padding: 2px 6px; border-radius: 6px; }
    .tag-green { color: #16a34a; }

    /* Interactive Stepper Controls */
    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
      margin-top: 12px;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      color: #334155;
      font-size: 13px;
      font-weight: 700;
      padding: 7px 14px;
      border-radius: 20px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
      transition: all 0.2s ease;
    }

    .step-btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
      box-shadow: 0 2px 8px rgba(2, 132, 199, 0.3);
    }

    .play-btn {
      background: #1e2945;
      color: #ffffff;
      border: none;
      border-radius: 50%;
      width: 34px;
      height: 34px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 13px;
      cursor: pointer;
      margin-left: 4px;
    }

    /* Animated SVG Elements */
    .jump-path {
      stroke-dasharray: 200;
      stroke-dashoffset: 200;
      transition: stroke-dashoffset 0.6s ease;
    }
    .jump-path.drawn {
      stroke-dashoffset: 0;
    }

    .jump-label {
      opacity: 0;
      transition: opacity 0.3s ease;
    }
    .jump-label.visible {
      opacity: 1;
    }

    .character {
      transition: transform 0.6s cubic-bezier(0.34, 1.56, 0.64, 1);
    }
  </style>
</head>
<body>

  <div class="header-pill">Make a Friendly Ten</div>

  <div class="main-stage">
    
    <div class="svg-container">
      <svg viewBox="0 0 600 180" id="numberLine">
        <defs>
          <marker id="arrow-blue" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
            <path d="M0,0 L6,3 L0,6 Z" fill="#0284c7" />
          </marker>
          <marker id="arrow-green" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
            <path d="M0,0 L6,3 L0,6 Z" fill="#16a34a" />
          </marker>
        </defs>

        
        <line x1="30" y1="120" x2="570" y2="120" stroke="#cbd5e1" stroke-width="4" stroke-linecap="round" />

        
        <rect x="278" y="100" width="44" height="68" rx="8" fill="#fef3c7" stroke="#f59e0b" stroke-width="1.5" stroke-dasharray="3,3" />

        
        
        <line x1="50" y1="112" x2="50" y2="128" stroke="#94a3b8" stroke-width="2" />
        <text x="50" y="148" text-anchor="middle" font-size="13" font-weight="600" fill="#64748b">245</text>

        
        <line x1="100" y1="114" x2="100" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="100" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">246</text>

        
        <line x1="150" y1="114" x2="150" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="150" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">247</text>

        
        <line x1="200" y1="110" x2="200" y2="130" stroke="#0284c7" stroke-width="3" />
        <text x="200" y="148" text-anchor="middle" font-size="14" font-weight="800" fill="#0284c7">248</text>

        
        <line x1="250" y1="114" x2="250" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="250" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">249</text>

        
        <line x1="300" y1="108" x2="300" y2="132" stroke="#d97706" stroke-width="3" />
        <text x="300" y="148" text-anchor="middle" font-size="15" font-weight="900" fill="#b45309">250</text>
        <text x="300" y="163" text-anchor="middle" font-size="10" font-weight="800" fill="#d97706">FRIENDLY 10</text>

        
        <line x1="350" y1="114" x2="350" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="350" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">251</text>

        
        <line x1="400" y1="114" x2="400" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="400" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">252</text>

        
        <line x1="450" y1="110" x2="450" y2="130" stroke="#16a34a" stroke-width="3" />
        <text x="450" y="148" text-anchor="middle" font-size="14" font-weight="800" fill="#16a34a">253</text>

        
        <line x1="500" y1="114" x2="500" y2="126" stroke="#cbd5e1" stroke-width="2" />
        <text x="500" y="148" text-anchor="middle" font-size="13" font-weight="500" fill="#94a3b8">254</text>

        
        <line x1="550" y1="112" x2="550" y2="128" stroke="#94a3b8" stroke-width="2" />
        <text x="550" y="148" text-anchor="middle" font-size="13" font-weight="600" fill="#64748b">255</text>

        
        
        <path id="jump1" class="jump-path" d="M 200 108 Q 250 45 296 108" fill="none" stroke="#0284c7" stroke-width="3.5" marker-end="url(#arrow-blue)" />
        <g id="label1" class="jump-label">
          <rect x="233" y="32" width="34" height="22" rx="6" fill="#0284c7" />
          <text x="250" y="47" text-anchor="middle" font-size="12" font-weight="800" fill="#ffffff">+2</text>
        </g>

        
        
        <path id="jump2" class="jump-path" d="M 300 108 Q 375 25 446 108" fill="none" stroke="#16a34a" stroke-width="3.5" marker-end="url(#arrow-green)" />
        <g id="label2" class="jump-label">
          <rect x="358" y="18" width="34" height="22" rx="6" fill="#16a34a" />
          <text x="375" y="33" text-anchor="middle" font-size="12" font-weight="800" fill="#ffffff">+3</text>
        </g>

        
        <g id="hero" class="character" transform="translate(200, 96)">
          <circle cx="0" cy="-14" r="15" fill="#3b82f6" />
          <text x="0" y="-8" text-anchor="middle" font-size="16">👾</text>
        </g>
      </svg>
    </div>

    
    <div class="split-card">
      <div class="split-tree">
        <div class="powerup-bubble">+5</div>
        <div class="branches">
          <div class="branch-pill branch-2" id="bond2">+2</div>
          <div class="branch-pill branch-3" id="bond3">+3</div>
        </div>
      </div>

      <div class="math-steps">
        <div class="math-row" id="row1">
          <span>248 + <span class="tag-blue">2</span> = <span class="tag-gold">250</span></span>
        </div>
        <div class="math-row" id="row2">
          <span>250 + <span class="tag-green">3</span> = <strong>253</strong></span>
        </div>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button class="step-btn active" id="btn0" onclick="setStep(0)">Start: 248</button>
    <button class="step-btn" id="btn1" onclick="setStep(1)">+2 to 250</button>
    <button class="step-btn" id="btn2" onclick="setStep(2)">+3 to 253</button>
    <button class="play-btn" id="playBtn" title="Auto Play" onclick="togglePlay()">▶</button>
  </div>

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

    const hero = document.getElementById('hero');
    const jump1 = document.getElementById('jump1');
    const label1 = document.getElementById('label1');
    const jump2 = document.getElementById('jump2');
    const label2 = document.getElementById('label2');
    const row1 = document.getElementById('row1');
    const row2 = document.getElementById('row2');
    const bond2 = document.getElementById('bond2');
    const bond3 = document.getElementById('bond3');
    const btns = [document.getElementById('btn0'), document.getElementById('btn1'), document.getElementById('btn2')];
    const playBtn = document.getElementById('playBtn');

    // Positions for character: 248 -> 200, 250 -> 300, 253 -> 450
    const charPositions = [200, 300, 450];

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

      // Character translation
      hero.setAttribute('transform', `translate(${charPositions[step]}, 96)`);

      if (step === 0) {
        jump1.classList.remove('drawn');
        label1.classList.remove('visible');
        jump2.classList.remove('drawn');
        label2.classList.remove('visible');
        row1.classList.remove('active');
        row2.classList.remove('active');
        bond2.style.opacity = '0.4';
        bond3.style.opacity = '0.4';
      } else if (step === 1) {
        jump1.classList.add('drawn');
        label1.classList.add('visible');
        jump2.classList.remove('drawn');
        label2.classList.remove('visible');
        row1.classList.add('active');
        row2.classList.remove('active');
        bond2.style.opacity = '1';
        bond3.style.opacity = '0.4';
      } else if (step === 2) {
        jump1.classList.add('drawn');
        label1.classList.add('visible');
        jump2.classList.add('drawn');
        label2.classList.add('visible');
        row1.classList.add('active');
        row2.classList.add('active');
        bond2.style.opacity = '1';
        bond3.style.opacity = '1';
      }
    }

    function togglePlay() {
      if (timer) {
        clearInterval(timer);
        timer = null;
        playBtn.textContent = '▶';
      } else {
        playBtn.textContent = '⏸';
        timer = setInterval(() => {
          let next = (currentStep + 1) % 3;
          setStep(next);
        }, 2600);
      }
    }

    // Initialize
    setStep(0);
    // Auto start calm loop after short delay
    setTimeout(() => {
      togglePlay();
    }, 800);
  </script>
</body>
</html>

OGM.4.NBT.4

Aligned learning resources

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