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Tutor model

i62 💰:9.4

i52 💰:7.9

🏆 i67 💰:62.5

i70 💰:125.0

i68 💰:125.0

🏆 i66 💰:75.0

i65 💰:125.0

i63 💰:62.5

i61 💰:75.0

i60 💰:9.4

i60 💰:37.5

i58 💰:62.5

i57 💰:22.5

i57 💰:37.5

i56 💰:45.0

⚡ i55 💰:11.25

i55 💰:37.5

i54 💰:62.5

i52 💰:35.0

i51 💰:37.5

i49 💰:15.0

i49 💰:62.5

i48 💰:11.3

i47 💰:7.5

i44 💰:25.0

i43 💰:37.5

i42 💰:187.5

i40 💰:5.0

i39 💰:100.0

i38 💰:37.5

i37 💰:11.0

i36 💰:187.5

i34 💰:12.5

i33 💰:37.5

i30 💰:1.0

i29 💰:1.5

i28 💰:150.0

i23 💰:20.0

i20 💰:4.0

i18 💰:1.0

i16 💰:25.0

i13 💰:1.5

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What would you like to learn?

Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

Lesson generation model

System default

i58 💰:18.8

i31 💰:11.0

i25 💰:31.3

Tutoring abilities

Imagine you have 28 shiny marbles in a jar. If someone asks how many you have, saying "about 30" is super fast and easy to picture!

**Rounding** means replacing a number with a friendlier number that is close to it, usually ending in zero.

<!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: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      user-select: none;
      -webkit-user-select: none;
    }

    body {
      padding: 16px;
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .main {
      width: 100%;
      max-width: 520px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 20px;
    }

    .tabs {
      display: flex;
      gap: 8px;
      background: #eef2f6;
      padding: 4px;
      border-radius: 12px;
      width: 100%;
      max-width: 380px;
    }

    .tab-btn {
      flex: 1;
      border: none;
      background: transparent;
      padding: 8px 6px;
      font-size: 14px;
      font-weight: 600;
      color: #6b7280;
      border-radius: 8px;
      cursor: pointer;
      transition: all 0.2s ease;
      text-align: center;
    }

    .tab-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 2px 6px rgba(0, 0, 0, 0.08);
    }

    .display-card {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 16px;
      font-size: 32px;
      font-weight: 700;
      background: #ffffff;
      padding: 12px 24px;
      border-radius: 16px;
      box-shadow: 0 4px 16px rgba(0, 0, 0, 0.05);
      border: 1px solid #e5e7eb;
      min-width: 260px;
      height: 64px;
    }

    .num-current {
      color: #1e2945;
      transition: color 0.2s ease;
    }

    .approx-symbol {
      color: #9ca3af;
      font-weight: 400;
    }

    .num-rounded {
      color: #0284c7;
      background: #e0f2fe;
      padding: 2px 12px;
      border-radius: 10px;
      transition: all 0.2s ease;
    }

    .line-container {
      width: 100%;
      padding: 20px 24px 36px 24px;
      position: relative;
    }

    .track {
      position: relative;
      height: 8px;
      background: #e5e7eb;
      border-radius: 999px;
      width: 100%;
    }

    .fill-left, .fill-right {
      position: absolute;
      top: 0;
      height: 100%;
      border-radius: 999px;
      transition: width 0.05s linear, left 0.05s linear;
    }

    .fill-active {
      background: #38bdf8;
    }

    .fill-inactive {
      background: #e5e7eb;
    }

    .pin {
      position: absolute;
      top: 50%;
      transform: translate(-50%, -50%);
      width: 24px;
      height: 24px;
      background: #0284c7;
      border: 3px solid #ffffff;
      box-shadow: 0 2px 8px rgba(2, 132, 199, 0.4);
      border-radius: 50%;
      z-index: 5;
      cursor: grab;
      pointer-events: none;
      transition: left 0.05s linear;
    }

    .pin-label {
      position: absolute;
      bottom: 28px;
      left: 50%;
      transform: translateX(-50%);
      background: #1e2945;
      color: #ffffff;
      font-size: 13px;
      font-weight: 700;
      padding: 3px 8px;
      border-radius: 6px;
      white-space: nowrap;
      pointer-events: none;
    }

    .pin-label::after {
      content: '';
      position: absolute;
      top: 100%;
      left: 50%;
      transform: translateX(-50%);
      border: 4px solid transparent;
      border-top-color: #1e2945;
    }

    .mid-marker {
      position: absolute;
      left: 50%;
      top: -8px;
      bottom: -8px;
      width: 2px;
      background: #cbd5e1;
      border-radius: 1px;
      transform: translateX(-50%);
    }

    .mid-label {
      position: absolute;
      top: calc(100% + 8px);
      left: 50%;
      transform: translateX(-50%);
      font-size: 12px;
      font-weight: 600;
      color: #94a3b8;
      white-space: nowrap;
    }

    .bench-label {
      position: absolute;
      top: calc(100% + 8px);
      font-size: 14px;
      font-weight: 700;
      color: #64748b;
      transition: color 0.2s ease;
    }

    .bench-label.left {
      left: 0;
      transform: translateX(-20%);
    }

    .bench-label.right {
      right: 0;
      transform: translateX(20%);
    }

    .bench-label.target {
      color: #0284c7;
    }

    .bench-tick {
      position: absolute;
      top: -6px;
      width: 4px;
      height: 20px;
      background: #94a3b8;
      border-radius: 2px;
    }

    .bench-tick.left {
      left: 0;
      transform: translateX(-50%);
    }

    .bench-tick.right {
      right: 0;
      transform: translateX(50%);
    }

    .slider {
      position: absolute;
      top: 0;
      left: 24px;
      right: 24px;
      width: calc(100% - 48px);
      height: 100%;
      opacity: 0;
      cursor: ew-resize;
      z-index: 10;
      margin: 0;
    }

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

    .preset-btn {
      background: #ffffff;
      border: 1px solid #e5e7eb;
      border-radius: 8px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: all 0.15s ease;
    }

    .preset-btn:hover {
      border-color: #38bdf8;
      color: #0284c7;
    }
  </style>
</head>
<body>
  <div class="main">
    <div class="tabs">
      <button class="tab-btn active" onclick="setMode(10)">10</button>
      <button class="tab-btn" onclick="setMode(100)">100</button>
      <button class="tab-btn" onclick="setMode(1000)">1,000</button>
    </div>

    <div class="display-card">
      <span class="num-current" id="curVal">67</span>
      <span class="approx-symbol">≈</span>
      <span class="num-rounded" id="roundVal">70</span>
    </div>

    <div class="line-container">
      <div class="track" id="track">
        <div class="bench-tick left"></div>
        <div class="bench-tick right"></div>
        <div class="mid-marker"></div>

        <div class="fill-left" id="fillLeft"></div>
        <div class="fill-right" id="fillRight"></div>

        <div class="pin" id="pin">
          <div class="pin-label" id="pinLabel">67</div>
        </div>

        <div class="bench-label left" id="lblLeft">60</div>
        <div class="mid-label" id="lblMid">65</div>
        <div class="bench-label right" id="lblRight">70</div>
      </div>

      <input type="range" class="slider" id="slider" min="0" max="100" value="70">
    </div>

    <div class="presets" id="presetGroup"></div>
  </div>

  <script>
    const CONFIG = {
      10: {
        min: 60,
        max: 70,
        step: 1,
        defaultVal: 67,
        presets: [62, 65, 68]
      },
      100: {
        min: 300,
        max: 400,
        step: 1,
        defaultVal: 340,
        presets: [320, 350, 380]
      },
      1000: {
        min: 4000,
        max: 5000,
        step: 10,
        defaultVal: 4600,
        presets: [4300, 4500, 4800]
      }
    };

    let currentScale = 10;
    let currentValue = 67;

    const slider = document.getElementById('slider');
    const curVal = document.getElementById('curVal');
    const roundVal = document.getElementById('roundVal');
    const pin = document.getElementById('pin');
    const pinLabel = document.getElementById('pinLabel');
    const lblLeft = document.getElementById('lblLeft');
    const lblMid = document.getElementById('lblMid');
    const lblRight = document.getElementById('lblRight');
    const fillLeft = document.getElementById('fillLeft');
    const fillRight = document.getElementById('fillRight');
    const presetGroup = document.getElementById('presetGroup');

    function formatNumber(n) {
      return n.toLocaleString();
    }

    function setMode(scale) {
      currentScale = scale;
      const conf = CONFIG[scale];
      
      document.querySelectorAll('.tab-btn').forEach((btn, idx) => {
        const scales = [10, 100, 1000];
        btn.classList.toggle('active', scales[idx] === scale);
      });

      slider.min = conf.min;
      slider.max = conf.max;
      slider.step = conf.step;
      slider.value = conf.defaultVal;

      lblLeft.textContent = formatNumber(conf.min);
      lblMid.textContent = formatNumber(conf.min + (conf.max - conf.min) / 2);
      lblRight.textContent = formatNumber(conf.max);

      presetGroup.innerHTML = '';
      conf.presets.forEach(p => {
        const btn = document.createElement('button');
        btn.className = 'preset-btn';
        btn.textContent = formatNumber(p);
        btn.onclick = () => {
          slider.value = p;
          update();
        };
        presetGroup.appendChild(btn);
      });

      update();
    }

    function update() {
      const conf = CONFIG[currentScale];
      const val = parseFloat(slider.value);
      const min = conf.min;
      const max = conf.max;
      const mid = min + (max - min) / 2;
      const pct = ((val - min) / (max - min)) * 100;

      const rounded = val >= mid ? max : min;

      curVal.textContent = formatNumber(val);
      roundVal.textContent = formatNumber(rounded);
      pinLabel.textContent = formatNumber(val);

      pin.style.left = `${pct}%`;

      if (val >= mid) {
        fillLeft.style.display = 'none';
        fillRight.style.display = 'block';
        fillRight.style.left = `${pct}%`;
        fillRight.style.width = `${100 - pct}%`;
        fillRight.className = 'fill-right fill-active';
        lblRight.classList.add('target');
        lblLeft.classList.remove('target');
      } else {
        fillRight.style.display = 'none';
        fillLeft.style.display = 'block';
        fillLeft.style.left = '0%';
        fillLeft.style.width = `${pct}%`;
        fillLeft.className = 'fill-left fill-active';
        lblLeft.classList.add('target');
        lblRight.classList.remove('target');
      }
    }

    slider.addEventListener('input', update);
    setMode(10);
  </script>
</body>
</html>

How do we know whether to round up or round down? Let's zoom in on the friendly rule.

Think of numbers on a roller coaster hill. Numbers 1, 2, 3, and 4 roll back down, while 5, 6, 7, 8, and 9 roll forward to the next ten.

<!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: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      padding: 12px;
      user-select: none;
      -webkit-user-select: none;
    }
    .diagram-root {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
      max-width: 540px;
      margin: 0 auto;
    }
    .mode-bar {
      display: flex;
      gap: 6px;
      background: #eef2f6;
      padding: 4px;
      border-radius: 20px;
    }
    .mode-btn {
      border: none;
      background: transparent;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #6b7280;
      border-radius: 16px;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .mode-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 2px 4px rgba(0,0,0,0.06);
    }
    .stage {
      position: relative;
      width: 100%;
      background: #ffffff;
      border-radius: 16px;
      box-shadow: 0 4px 12px rgba(0,0,0,0.04);
      padding: 12px 10px 8px 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
    }
    .result-badge {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 18px;
      font-weight: 700;
      padding: 6px 16px;
      border-radius: 20px;
      margin-bottom: 4px;
      transition: all 0.3s ease;
    }
    .badge-down {
      background: #fef3c7;
      color: #b45309;
    }
    .badge-up {
      background: #e0f2fe;
      color: #0369a1;
    }
    .badge-neutral {
      background: #f1f5f9;
      color: #475569;
    }
    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }
    .hill-path {
      fill: none;
      stroke: #e2e8f0;
      stroke-width: 6;
      stroke-linecap: round;
    }
    .hill-fill {
      fill: #f8fafc;
    }
    .zone-down {
      fill: none;
      stroke: #f59e0b;
      stroke-width: 6;
      stroke-linecap: round;
      opacity: 0.85;
    }
    .zone-up {
      fill: none;
      stroke: #0284c7;
      stroke-width: 6;
      stroke-linecap: round;
      opacity: 0.85;
    }
    .node-point {
      cursor: pointer;
      transition: r 0.2s ease, fill 0.2s ease;
    }
    .node-point:hover {
      r: 9;
    }
    .node-text {
      font-size: 12px;
      font-weight: 600;
      fill: #64748b;
      text-anchor: middle;
      pointer-events: none;
    }
    .node-text.active {
      fill: #0f172a;
      font-weight: 800;
    }
    .cart {
      transition: transform 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
      cursor: grab;
    }
    .stepper-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      width: 100%;
      padding-top: 4px;
    }
    .digit-btn {
      flex: 1;
      max-width: 38px;
      height: 34px;
      border: 1px solid #e2e8f0;
      background: #ffffff;
      border-radius: 8px;
      font-size: 14px;
      font-weight: 700;
      color: #475569;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .digit-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 6px rgba(2,132,199,0.3);
    }
    .digit-btn.down.active {
      background: #f59e0b;
      border-color: #f59e0b;
      box-shadow: 0 2px 6px rgba(245,158,11,0.3);
    }
    .zone-label {
      font-size: 12px;
      font-weight: 700;
      letter-spacing: 0.5px;
    }
    .rule-pill {
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      background: #f1f5f9;
      padding: 4px 12px;
      border-radius: 12px;
      margin-top: 2px;
    }
  </style>
</head>
<body>
  <div class="diagram-root">
    <div class="mode-bar">
      <button class="mode-btn active" data-scale="10">Nearest 10</button>
      <button class="mode-btn" data-scale="100">Nearest 100</button>
      <button class="mode-btn" data-scale="1000">Nearest 1000</button>
    </div>

    <div class="stage">
      <div id="resultBadge" class="result-badge badge-neutral">
        <span id="fromVal">43</span>
        <span id="arrowIcon">→</span>
        <span id="toVal">40</span>
      </div>

      <svg viewBox="0 0 460 190" id="hillSvg">
        <defs>
          <linearGradient id="hillShade" x1="0" y1="0" x2="0" y2="1">
            <stop offset="0%" stop-color="#f1f5f9" stop-opacity="0.8"/>
            <stop offset="100%" stop-color="#ffffff" stop-opacity="0"/>
          </linearGradient>
        </defs>

        <path id="hillFill" class="hill-fill" />
        <path id="leftZone" class="zone-down" />
        <path id="rightZone" class="zone-up" />

        <text x="70" y="55" class="zone-label" fill="#d97706" text-anchor="middle">↙ 1, 2, 3, 4 DOWN</text>
        <text x="380" y="55" class="zone-label" fill="#0284c7" text-anchor="middle">5, 6, 7, 8, 9 UP ↗</text>

        <g id="pointsGroup"></g>

        
        <g id="cartGroup" class="cart">
          <circle cx="0" cy="0" r="14" fill="#1e2945" />
          <circle cx="0" cy="0" r="6" fill="#ffffff" />
          <text id="cartLabel" x="0" y="4" font-size="10" font-weight="800" fill="#1e2945" text-anchor="middle"></text>
        </g>
      </svg>

      <div class="stepper-bar" id="stepperBar"></div>
      <div class="rule-pill" id="rulePill">4 rolls down to 40</div>
    </div>
  </div>

  <script>
    const P_X = [40, 78, 116, 154, 192, 230, 268, 306, 344, 382, 420];
    const BASE_Y = 160;
    const PEAK_Y = 65;

    function calcY(t) {
      const s = Math.sin((t / 10) * Math.PI);
      return BASE_Y - (BASE_Y - PEAK_Y) * Math.pow(s, 1.4);
    }

    const points = P_X.map((x, i) => ({ x, y: calcY(i) }));

    function buildSpline(pts) {
      let d = `M ${pts[0].x} ${pts[0].y}`;
      for (let i = 0; i < pts.length - 1; i++) {
        const p0 = pts[i === 0 ? 0 : i - 1];
        const p1 = pts[i];
        const p2 = pts[i + 1];
        const p3 = pts[i + 2] || p2;
        const cp1x = p1.x + (p2.x - p0.x) / 6;
        const cp1y = p1.y + (p2.y - p0.y) / 6;
        const cp2x = p2.x - (p3.x - p1.x) / 6;
        const cp2y = p2.y - (p3.y - p1.y) / 6;
        d += ` C ${cp1x} ${cp1y}, ${cp2x} ${cp2y}, ${p2.x} ${p2.y}`;
      }
      return d;
    }

    const fullPath = buildSpline(points);
    const leftPath = buildSpline(points.slice(0, 6));
    const rightPath = buildSpline(points.slice(5));

    document.getElementById('hillFill').setAttribute('d', fullPath + ` L ${points[10].x} ${BASE_Y + 15} L ${points[0].x} ${BASE_Y + 15} Z`);
    document.getElementById('leftZone').setAttribute('d', leftPath);
    document.getElementById('rightZone').setAttribute('d', rightPath);

    const ptsGroup = document.getElementById('pointsGroup');
    points.forEach((pt, i) => {
      const g = document.createElementNS('http://www.w3.org/2000/svg', 'g');
      
      const c = document.createElementNS('http://www.w3.org/2000/svg', 'circle');
      c.setAttribute('cx', pt.x);
      c.setAttribute('cy', pt.y);
      c.setAttribute('r', i === 5 ? 7 : (i === 0 || i === 10 ? 6 : 5));
      c.setAttribute('fill', i === 0 || i === 10 ? '#64748b' : (i < 5 ? '#f59e0b' : '#0284c7'));
      c.setAttribute('class', 'node-point');
      c.onclick = () => selectDigit(i);

      const t = document.createElementNS('http://www.w3.org/2000/svg', 'text');
      t.setAttribute('x', pt.x);
      t.setAttribute('y', pt.y + (i === 5 ? -14 : (i === 0 || i === 10 ? 18 : (pt.y < 100 ? -12 : 18))));
      t.setAttribute('class', 'node-text');
      t.id = 'nodeText' + i;
      t.textContent = i;

      g.appendChild(c);
      g.appendChild(t);
      ptsGroup.appendChild(g);
    });

    const stepperBar = document.getElementById('stepperBar');
    for (let i = 0; i <= 10; i++) {
      const b = document.createElement('button');
      b.className = 'digit-btn' + (i < 5 ? ' down' : '');
      b.textContent = i;
      b.onclick = () => selectDigit(i);
      b.id = 'digitBtn' + i;
      stepperBar.appendChild(b);
    }

    let currentScale = 10;
    let currentDigit = 3;

    const baseMap = {
      10: { prefix: 4, mul: 1, baseLow: 40, baseHigh: 50 },
      100: { prefix: 4, mul: 10, baseLow: 400, baseHigh: 500 },
      1000: { prefix: 4, mul: 100, baseLow: 4000, baseHigh: 5000 }
    };

    function update() {
      const cfg = baseMap[currentScale];
      let val = (cfg.prefix * currentScale) + (currentDigit * (currentScale / 10));
      let rounded = currentDigit < 5 ? cfg.baseLow : cfg.baseHigh;

      const fromSpan = document.getElementById('fromVal');
      const toSpan = document.getElementById('toVal');
      const badge = document.getElementById('resultBadge');
      const pill = document.getElementById('rulePill');

      fromSpan.textContent = val.toLocaleString();
      toSpan.textContent = rounded.toLocaleString();

      if (currentDigit === 0 || currentDigit === 10) {
        badge.className = 'result-badge badge-neutral';
        pill.textContent = `${val.toLocaleString()} is exact`;
      } else if (currentDigit < 5) {
        badge.className = 'result-badge badge-down';
        pill.textContent = `${currentDigit} < 5 → Round DOWN to ${rounded.toLocaleString()}`;
      } else if (currentDigit === 5) {
        badge.className = 'result-badge badge-up';
        pill.textContent = `5 is halfway → Round UP to ${rounded.toLocaleString()}`;
      } else {
        badge.className = 'result-badge badge-up';
        pill.textContent = `${currentDigit} ≥ 5 → Round UP to ${rounded.toLocaleString()}`;
      }

      const pt = points[currentDigit];
      const cart = document.getElementById('cartGroup');
      cart.style.transform = `translate(${pt.x}px, ${pt.y}px)`;

      for (let i = 0; i <= 10; i++) {
        const btn = document.getElementById('digitBtn' + i);
        const txt = document.getElementById('nodeText' + i);
        if (i === currentDigit) {
          btn.classList.add('active');
          txt.classList.add('active');
        } else {
          btn.classList.remove('active');
          txt.classList.remove('active');
        }
      }
    }

    function selectDigit(d) {
      currentDigit = d;
      update();
    }

    document.querySelectorAll('.mode-btn').forEach(btn => {
      btn.onclick = () => {
        document.querySelectorAll('.mode-btn').forEach(b => b.classList.remove('active'));
        btn.classList.add('active');
        currentScale = parseInt(btn.dataset.scale, 10);
        update();
      };
    });

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

If a number lands right in the middle on **5**, the rule in math is to always round **up**.

Let's see what happens when we round two-digit numbers to the nearest 10.

To round to the nearest ten, underline the **tens place** and look at the **ones digit** directly to its right.

Let's round **43** to the nearest 10. The ones digit is 3, which is less than 5, so 43 rounds down to **40**.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Rounding Visualizer</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
      user-select: none;
      -webkit-user-select: none;
    }

    body {
      background: #f8f9fa;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .main-wrap {
      width: 100%;
      max-width: 520px;
      display: flex;
      flex-direction: column;
      gap: 16px;
      align-items: center;
    }

    /* Mode Tabs */
    .tabs {
      display: flex;
      background: #e9ecef;
      padding: 4px;
      border-radius: 20px;
      gap: 4px;
      width: 100%;
      max-width: 360px;
    }

    .tab-btn {
      flex: 1;
      border: none;
      background: transparent;
      padding: 8px 0;
      font-size: 14px;
      font-weight: 600;
      color: #6c757d;
      border-radius: 16px;
      cursor: pointer;
      transition: all 0.2s ease;
      text-align: center;
    }

    .tab-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 2px 6px rgba(0,0,0,0.08);
    }

    /* Equation Display */
    .display-panel {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 14px;
      font-size: 32px;
      font-weight: 700;
      height: 48px;
    }

    .val-current {
      color: #0284c7;
      min-width: 80px;
      text-align: right;
    }

    .arrow-sym {
      color: #94a3b8;
      font-size: 24px;
    }

    .val-rounded {
      color: #059669;
      min-width: 80px;
      text-align: left;
      background: #d1fae5;
      padding: 2px 12px;
      border-radius: 10px;
      transition: all 0.2s ease;
    }

    /* Number Line Canvas Container */
    .line-container {
      width: 100%;
      background: #ffffff;
      border-radius: 16px;
      padding: 24px 20px 20px 20px;
      box-shadow: 0 4px 12px rgba(0,0,0,0.04);
      position: relative;
    }

    svg {
      width: 100%;
      height: 90px;
      display: block;
      overflow: visible;
    }

    /* Slider control */
    .slider-wrap {
      width: 100%;
      padding: 0 6px;
      margin-top: 8px;
    }

    input[type="range"] {
      -webkit-appearance: none;
      appearance: none;
      width: 100%;
      height: 8px;
      background: #e2e8f0;
      border-radius: 4px;
      outline: none;
      cursor: pointer;
    }

    input[type="range"]::-webkit-slider-thumb {
      -webkit-appearance: none;
      appearance: none;
      width: 28px;
      height: 28px;
      border-radius: 50%;
      background: #0284c7;
      border: 3px solid #ffffff;
      box-shadow: 0 2px 8px rgba(2, 132, 199, 0.4);
      cursor: grab;
      transition: transform 0.1s;
    }

    input[type="range"]::-webkit-slider-thumb:active {
      cursor: grabbing;
      transform: scale(1.1);
    }

    input[type="range"]::-moz-range-thumb {
      width: 28px;
      height: 28px;
      border-radius: 50%;
      background: #0284c7;
      border: 3px solid #ffffff;
      box-shadow: 0 2px 8px rgba(2, 132, 199, 0.4);
      cursor: grab;
    }

    /* Quick jump pills */
    .pills {
      display: flex;
      gap: 8px;
      flex-wrap: wrap;
      justify-content: center;
    }

    .pill-btn {
      border: 1px solid #cbd5e1;
      background: #ffffff;
      padding: 5px 12px;
      border-radius: 12px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: all 0.15s ease;
    }

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

    .pill-btn.active {
      background: #e0f2fe;
      border-color: #38bdf8;
      color: #0284c7;
    }
  </style>
</head>
<body>

  <div class="main-wrap">
    
    <div class="tabs">
      <button class="tab-btn active" onclick="setMode('10')">Nearest 10</button>
      <button class="tab-btn" onclick="setMode('100')">Nearest 100</button>
      <button class="tab-btn" onclick="setMode('1000')">Nearest 1000</button>
    </div>

    
    <div class="display-panel">
      <span class="val-current" id="curNum">43</span>
      <span class="arrow-sym">≈</span>
      <span class="val-rounded" id="roundNum">40</span>
    </div>

    
    <div class="line-container">
      <svg id="svgLine" viewBox="0 0 400 90">
        
        <line x1="30" y1="45" x2="370" y2="45" stroke="#e2e8f0" stroke-width="8" stroke-linecap="round"/>
        
        
        <line id="roundDownTrack" x1="30" y1="45" x2="200" y2="45" stroke="#f1f5f9" stroke-width="6"/>
        <line id="roundUpTrack" x1="200" y1="45" x2="370" y2="45" stroke="#ecfdf5" stroke-width="6"/>

        
        <line x1="30" y1="35" x2="30" y2="55" stroke="#64748b" stroke-width="3" stroke-linecap="round"/>
        <line x1="200" y1="38" x2="200" y2="52" stroke="#f59e0b" stroke-width="3" stroke-linecap="round" stroke-dasharray="3,3"/>
        <line x1="370" y1="35" x2="370" y2="55" stroke="#64748b" stroke-width="3" stroke-linecap="round"/>

        
        <path id="snapArc" d="M 132 45 Q 81 20 30 45" fill="none" stroke="#0284c7" stroke-width="2.5" stroke-dasharray="4,4" opacity="0.8"/>

        
        <text id="lblMin" x="30" y="75" font-size="14" font-weight="700" fill="#475569" text-anchor="middle">40</text>
        <text id="lblMid" x="200" y="75" font-size="13" font-weight="700" fill="#d97706" text-anchor="middle">45</text>
        <text id="lblMax" x="370" y="75" font-size="14" font-weight="700" fill="#475569" text-anchor="middle">50</text>

        
        <g id="markerGroup" transform="translate(132, 45)">
          <circle r="9" fill="#0284c7" stroke="#ffffff" stroke-width="2.5" />
          <circle r="15" fill="#0284c7" opacity="0.2"/>
        </g>
      </svg>

      <div class="slider-wrap">
        <input type="range" id="numSlider" min="40" max="50" value="43" step="1" oninput="onSlide(this.value)">
      </div>
    </div>

    
    <div class="pills" id="pillsContainer"></div>
  </div>

  <script>
    const MODES = {
      '10': {
        min: 40,
        max: 50,
        mid: 45,
        default: 43,
        step: 1,
        pills: [41, 43, 45, 47]
      },
      '100': {
        min: 300,
        max: 400,
        mid: 350,
        default: 340,
        step: 5,
        pills: [320, 340, 350, 380]
      },
      '1000': {
        min: 4000,
        max: 5000,
        mid: 4500,
        default: 4600,
        step: 50,
        pills: [4200, 4450, 4500, 4800]
      }
    };

    let currentMode = '10';

    function setMode(modeKey) {
      currentMode = modeKey;
      
      // Update tab buttons
      document.querySelectorAll('.tab-btn').forEach((btn, idx) => {
        btn.classList.toggle('active', (modeKey === '10' && idx === 0) || (modeKey === '100' && idx === 1) || (modeKey === '1000' && idx === 2));
      });

      const config = MODES[modeKey];
      const slider = document.getElementById('numSlider');
      slider.min = config.min;
      slider.max = config.max;
      slider.step = config.step;
      slider.value = config.default;

      // Update base labels
      document.getElementById('lblMin').textContent = config.min;
      document.getElementById('lblMid').textContent = config.mid;
      document.getElementById('lblMax').textContent = config.max;

      // Render pills
      const pillsContainer = document.getElementById('pillsContainer');
      pillsContainer.innerHTML = '';
      config.pills.forEach(val => {
        const btn = document.createElement('button');
        btn.className = 'pill-btn';
        btn.textContent = val;
        btn.onclick = () => {
          slider.value = val;
          update(val);
        };
        pillsContainer.appendChild(btn);
      });

      update(config.default);
    }

    function roundValue(val, mode) {
      const step = parseInt(mode, 10);
      return Math.round(val / step) * step;
    }

    function onSlide(val) {
      update(Number(val));
    }

    function update(val) {
      const config = MODES[currentMode];
      const rounded = roundValue(val, currentMode);

      document.getElementById('curNum').textContent = val;
      document.getElementById('roundNum').textContent = rounded;

      // Highlight matching pill
      document.querySelectorAll('.pill-btn').forEach(btn => {
        btn.classList.toggle('active', Number(btn.textContent) === val);
      });

      // SVG calculations (track from x=30 to x=370, total width 340)
      const ratio = (val - config.min) / (config.max - config.min);
      const markerX = 30 + ratio * 340;

      // Move marker
      const markerGroup = document.getElementById('markerGroup');
      markerGroup.setAttribute('transform', `translate(${markerX}, 45)`);

      // Snap arc
      const targetX = rounded === config.min ? 30 : 370;
      const snapArc = document.getElementById('snapArc');
      
      if (val === config.min || val === config.max) {
        snapArc.setAttribute('opacity', '0');
      } else {
        snapArc.setAttribute('opacity', '0.85');
        const midArcX = (markerX + targetX) / 2;
        const controlY = 45 - Math.min(30, Math.abs(markerX - targetX) * 0.22);
        snapArc.setAttribute('d', `M ${markerX} 45 Q ${midArcX} ${controlY} ${targetX} 45`);
        snapArc.setAttribute('stroke', rounded >= config.mid ? '#059669' : '#0284c7');
      }
    }

    // Initialize
    setMode('10');
  </script>
</body>
</html>

What if we have a bigger number, like hundreds of building blocks?

When we round to the nearest hundred, we look at the **tens digit** to make our choice.

Take **320**. The middle number between 300 and 400 is 350. Since 320 is before 350, it rounds down to **300**.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="aspect-ratio" content="4:3">
<title>Rounding on a Number Line</title>
<style>
  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background: #f8f9fa;
    color: #1e2945;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    padding: 16px;
    user-select: none;
    -webkit-user-select: none;
  }

  .main-wrap {
    width: 100%;
    max-width: 580px;
    display: flex;
    flex-direction: column;
    gap: 16px;
  }

  /* Segmented Mode Selector */
  .mode-switch {
    display: flex;
    background: #eef2f6;
    border-radius: 10px;
    padding: 4px;
    gap: 4px;
  }
  .mode-btn {
    flex: 1;
    border: none;
    background: transparent;
    padding: 8px 12px;
    border-radius: 8px;
    font-size: 14px;
    font-weight: 600;
    color: #64748b;
    cursor: pointer;
    transition: all 0.2s ease;
  }
  .mode-btn.active {
    background: #ffffff;
    color: #0284c7;
    box-shadow: 0 2px 6px rgba(0,0,0,0.06);
  }

  /* Display Result Panel */
  .display-box {
    background: #ffffff;
    border-radius: 14px;
    padding: 18px 20px;
    box-shadow: 0 4px 16px rgba(0,0,0,0.04);
    border: 1px solid #e2e8f0;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  .val-block {
    display: flex;
    flex-direction: column;
  }
  .val-lbl {
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    color: #64748b;
    font-weight: 700;
  }
  .val-num {
    font-size: 28px;
    font-weight: 800;
    color: #0f172a;
  }
  .round-arrow {
    font-size: 22px;
    color: #94a3b8;
  }
  .result-num {
    color: #0284c7;
  }

  /* Interactive Visual Track */
  .track-card {
    background: #ffffff;
    border-radius: 14px;
    padding: 24px 20px 20px;
    box-shadow: 0 4px 16px rgba(0,0,0,0.04);
    border: 1px solid #e2e8f0;
    position: relative;
  }

  .number-line-container {
    position: relative;
    height: 90px;
    margin: 0 10px;
  }

  /* Benchmark markers */
  .line-bar {
    position: absolute;
    top: 36px;
    left: 0;
    right: 0;
    height: 8px;
    background: #e2e8f0;
    border-radius: 4px;
  }
  .line-fill-down {
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    background: #cbd5e1;
    border-radius: 4px 0 0 4px;
  }
  .line-fill-up {
    position: absolute;
    right: 0;
    top: 0;
    height: 100%;
    background: #bae6fd;
    border-radius: 0 4px 4px 0;
  }

  .tick {
    position: absolute;
    top: 26px;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    font-size: 13px;
    font-weight: 700;
    color: #475569;
  }
  .tick-mark {
    width: 2px;
    height: 28px;
    background: #94a3b8;
    margin-bottom: 6px;
    border-radius: 1px;
  }
  .tick.mid .tick-mark {
    background: #f59e0b;
    height: 22px;
    border-style: dashed;
  }
  .tick.mid {
    color: #d97706;
  }
  .tick.active-target {
    color: #0284c7;
    font-weight: 800;
  }

  /* Draggable Pin */
  .pin {
    position: absolute;
    top: 0;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    cursor: grab;
    z-index: 10;
    transition: left 0.15s ease-out;
  }
  .pin:active {
    cursor: grabbing;
  }
  .pin-bubble {
    background: #0284c7;
    color: #ffffff;
    font-size: 14px;
    font-weight: 700;
    padding: 3px 10px;
    border-radius: 12px;
    box-shadow: 0 3px 8px rgba(2, 132, 199, 0.35);
    white-space: nowrap;
  }
  .pin-pointer {
    width: 14px;
    height: 14px;
    background: #0284c7;
    transform: rotate(45deg);
    margin-top: -7px;
    border-radius: 2px;
  }

  /* Range Slider */
  .slider-box {
    margin-top: 10px;
  }
  .range-slider {
    width: 100%;
    -webkit-appearance: none;
    appearance: none;
    height: 36px;
    background: transparent;
    cursor: pointer;
  }
  .range-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 26px;
    height: 26px;
    border-radius: 50%;
    background: #0284c7;
    box-shadow: 0 2px 6px rgba(0,0,0,0.25);
    border: 3px solid #ffffff;
    cursor: pointer;
  }
  .range-slider::-moz-range-thumb {
    width: 26px;
    height: 26px;
    border-radius: 50%;
    background: #0284c7;
    box-shadow: 0 2px 6px rgba(0,0,0,0.25);
    border: 3px solid #ffffff;
    cursor: pointer;
  }

  /* Quick-select chips */
  .chip-row {
    display: flex;
    justify-content: center;
    gap: 8px;
    margin-top: 12px;
  }
  .chip {
    border: 1px solid #cbd5e1;
    background: #f8fafc;
    border-radius: 20px;
    padding: 4px 12px;
    font-size: 13px;
    font-weight: 600;
    color: #475569;
    cursor: pointer;
    transition: all 0.15s ease;
  }
  .chip:hover {
    background: #e2e8f0;
    color: #0f172a;
  }
</style>
</head>
<body>

<div class="main-wrap">
  
  <div class="mode-switch">
    <button class="mode-btn" data-scale="10">Nearest 10</button>
    <button class="mode-btn active" data-scale="100">Nearest 100</button>
    <button class="mode-btn" data-scale="1000">Nearest 1000</button>
  </div>

  
  <div class="display-box">
    <div class="val-block">
      <span class="val-lbl">Number</span>
      <span class="val-num" id="currentVal">320</span>
    </div>
    <div class="round-arrow">➔</div>
    <div class="val-block" style="text-align: right;">
      <span class="val-lbl">Rounded</span>
      <span class="val-num result-num" id="roundedVal">300</span>
    </div>
  </div>

  
  <div class="track-card">
    <div class="number-line-container">
      <div class="line-bar">
        <div class="line-fill-down" id="fillDown" style="width: 50%;"></div>
        <div class="line-fill-up" id="fillUp" style="width: 50%;"></div>
      </div>

      
      <div class="tick" style="left: 0%;">
        <div class="tick-mark"></div>
        <span id="labelLow">300</span>
      </div>
      <div class="tick mid" style="left: 50%;">
        <div class="tick-mark"></div>
        <span id="labelMid">350</span>
      </div>
      <div class="tick" style="left: 100%;">
        <div class="tick-mark"></div>
        <span id="labelHigh">400</span>
      </div>

      
      <div class="pin" id="pin" style="left: 20%;">
        <div class="pin-bubble" id="pinLabel">320</div>
        <div class="pin-pointer"></div>
      </div>
    </div>

    
    <div class="slider-box">
      <input type="range" class="range-slider" id="scrubber" min="300" max="400" step="1" value="320">
    </div>

    
    <div class="chip-row" id="presetChips">
      
    </div>
  </div>
</div>

<script>
  const configs = {
    10: { min: 30, max: 40, mid: 35, start: 32, presets: [32, 35, 38] },
    100: { min: 300, max: 400, mid: 350, start: 320, presets: [320, 350, 375] },
    1000: { min: 3000, max: 4000, mid: 3500, start: 3200, presets: [3200, 3500, 3850] }
  };

  let currentScale = 100;

  const scrubber = document.getElementById('scrubber');
  const currentValEl = document.getElementById('currentVal');
  const roundedValEl = document.getElementById('roundedVal');
  const pin = document.getElementById('pin');
  const pinLabel = document.getElementById('pinLabel');
  const labelLow = document.getElementById('labelLow');
  const labelMid = document.getElementById('labelMid');
  const labelHigh = document.getElementById('labelHigh');
  const presetChips = document.getElementById('presetChips');

  function roundValue(val, scale) {
    return Math.round(val / scale) * scale;
  }

  function updateVisual(val) {
    const cfg = configs[currentScale];
    const pct = ((val - cfg.min) / (cfg.max - cfg.min)) * 100;
    
    pin.style.left = `${pct}%`;
    pinLabel.textContent = val;
    currentValEl.textContent = val;

    const rounded = roundValue(val, currentScale);
    roundedValEl.textContent = rounded;

    // Highlight target tick
    labelLow.parentElement.classList.toggle('active-target', rounded === cfg.min);
    labelHigh.parentElement.classList.toggle('active-target', rounded === cfg.max);
  }

  function setScale(scale) {
    currentScale = scale;
    const cfg = configs[scale];

    labelLow.textContent = cfg.min;
    labelMid.textContent = cfg.mid;
    labelHigh.textContent = cfg.max;

    scrubber.min = cfg.min;
    scrubber.max = cfg.max;
    scrubber.step = scale === 10 ? 1 : (scale === 100 ? 5 : 50);
    scrubber.value = cfg.start;

    // Render presets
    presetChips.innerHTML = '';
    cfg.presets.forEach(p => {
      const chip = document.createElement('button');
      chip.className = 'chip';
      chip.textContent = p;
      chip.onclick = () => {
        scrubber.value = p;
        updateVisual(p);
      };
      presetChips.appendChild(chip);
    });

    updateVisual(cfg.start);
  }

  // Event Listeners
  document.querySelectorAll('.mode-btn').forEach(btn => {
    btn.addEventListener('click', () => {
      document.querySelectorAll('.mode-btn').forEach(b => b.classList.remove('active'));
      btn.classList.add('active');
      setScale(Number(btn.dataset.scale));
    });
  });

  scrubber.addEventListener('input', (e) => {
    updateVisual(Number(e.target.value));
  });

  // Init
  setScale(100);
</script>

</body>
</html>

What happens if we look at huge numbers, like thousands of miles?

To round to the nearest thousand, look at the **hundreds digit** right next to the thousands place.

For **4,700**, the hundreds digit is 7. Because 7 is 5 or more, 4,700 rounds up to **5,000**!

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Rounding Whole Numbers</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      padding: 12px;
    }
    .main-wrap {
      width: 100%;
      max-width: 480px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    /* Mode Selector */
    .tabs {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 6px;
      background: #e9ecef;
      padding: 4px;
      border-radius: 12px;
    }
    .tab-btn {
      border: none;
      background: transparent;
      padding: 8px 4px;
      font-size: 13px;
      font-weight: 700;
      color: #6c757d;
      border-radius: 8px;
      cursor: pointer;
      transition: background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
      text-align: center;
      white-space: nowrap;
    }
    .tab-btn.active {
      background: #ffffff;
      color: #0b72b9;
      box-shadow: 0 2px 6px rgba(0,0,0,0.08);
    }
    /* Card Display */
    .display-card {
      background: #ffffff;
      border-radius: 16px;
      padding: 16px;
      box-shadow: 0 4px 16px rgba(0,0,0,0.05);
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 14px;
    }
    /* Digits Row */
    .digits-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      position: relative;
    }
    .digit-box {
      width: 46px;
      height: 58px;
      border-radius: 10px;
      background: #f1f5f9;
      border: 2px solid #e2e8f0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      position: relative;
      transition: background 0.3s ease, border-color 0.3s ease, box-shadow 0.3s ease;
    }
    .digit-val {
      font-size: 26px;
      font-weight: 800;
      line-height: 1;
      color: #1e2945;
    }
    .digit-label {
      font-size: 9px;
      font-weight: 700;
      text-transform: uppercase;
      color: #94a3b8;
      margin-top: 3px;
      letter-spacing: 0.5px;
    }
    .comma {
      font-size: 26px;
      font-weight: 800;
      color: #94a3b8;
      margin: 0 -2px;
      align-self: flex-end;
      padding-bottom: 8px;
    }
    /* Highlights */
    .digit-box.target {
      background: #e0f2fe;
      border-color: #0284c7;
      box-shadow: 0 0 0 2px rgba(2,132,199,0.25);
    }
    .digit-box.target .digit-val {
      color: #0369a1;
    }
    .digit-box.target .digit-label {
      color: #0284c7;
    }
    .digit-box.decider {
      background: #fef3c7;
      border-color: #f59e0b;
      box-shadow: 0 0 0 2px rgba(245,158,11,0.25);
    }
    .digit-box.decider .digit-val {
      color: #b45309;
    }
    .digit-box.decider .digit-label {
      color: #d97706;
    }
    /* Rule Badge / Decision */
    .decision-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      min-height: 38px;
    }
    .decision-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      padding: 6px 12px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 700;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
    }
    .decision-badge.up {
      background: #ecfdf5;
      border-color: #a7f3d0;
      color: #047857;
    }
    .decision-badge.down {
      background: #eff6ff;
      border-color: #bfdbfe;
      color: #1d4ed8;
    }
    /* Visual Number Line / Track */
    .track-wrap {
      width: 100%;
      padding: 0 8px;
    }
    .track-bar {
      position: relative;
      height: 8px;
      background: #e2e8f0;
      border-radius: 4px;
      margin: 20px 0 16px;
    }
    .track-progress {
      position: absolute;
      top: 0;
      left: 0;
      height: 100%;
      background: #38bdf8;
      border-radius: 4px;
      transition: width 0.4s ease;
    }
    .track-mid {
      position: absolute;
      top: -4px;
      left: 50%;
      transform: translateX(-50%);
      width: 2px;
      height: 16px;
      background: #94a3b8;
    }
    .track-marker {
      position: absolute;
      top: 50%;
      transform: translate(-50%, -50%);
      width: 18px;
      height: 18px;
      background: #0284c7;
      border: 3px solid #ffffff;
      border-radius: 50%;
      box-shadow: 0 2px 6px rgba(0,0,0,0.2);
      transition: left 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
    }
    .track-labels {
      display: flex;
      justify-content: space-between;
      font-size: 12px;
      font-weight: 700;
      color: #64748b;
    }
    .track-labels .active-bound {
      color: #0284c7;
      font-weight: 800;
    }
    /* Result Box */
    .result-box {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      padding: 8px 16px;
      background: #f8fafc;
      border-radius: 10px;
      width: 100%;
    }
    .arrow-trans {
      font-size: 16px;
      color: #94a3b8;
    }
    .res-val {
      font-size: 22px;
      font-weight: 800;
      color: #0284c7;
      letter-spacing: 0.5px;
    }
  </style>
</head>
<body>
  <div class="main-wrap">
    
    <div class="tabs">
      <button class="tab-btn" onclick="setMode(0)" id="btn-0">Nearest 10</button>
      <button class="tab-btn" onclick="setMode(1)" id="btn-1">Nearest 100</button>
      <button class="tab-btn active" onclick="setMode(2)" id="btn-2">Nearest 1000</button>
    </div>

    
    <div class="display-card">
      
      <div class="digits-row">
        <div class="digit-box" id="box-th">
          <span class="digit-val" id="d-th">4</span>
          <span class="digit-label">1000s</span>
        </div>
        <span class="comma">,</span>
        <div class="digit-box" id="box-h">
          <span class="digit-val" id="d-h">7</span>
          <span class="digit-label">100s</span>
        </div>
        <div class="digit-box" id="box-t">
          <span class="digit-val" id="d-t">3</span>
          <span class="digit-label">10s</span>
        </div>
        <div class="digit-box" id="box-o">
          <span class="digit-val" id="d-o">6</span>
          <span class="digit-label">1s</span>
        </div>
      </div>

      
      <div class="decision-row">
        <div class="decision-badge up" id="badge-rule">
          <span>7 ≥ 5</span>
          <span>➔</span>
          <span>Round Up (+1)</span>
        </div>
      </div>

      
      <div class="track-wrap">
        <div class="track-bar">
          <div class="track-progress" id="track-prog" style="width: 70%;"></div>
          <div class="track-mid"></div>
          <div class="track-marker" id="track-mark" style="left: 70%;"></div>
        </div>
        <div class="track-labels">
          <span id="bound-low">4,000</span>
          <span style="font-size: 10px; color: #94a3b8;">MID (5)</span>
          <span id="bound-high" class="active-bound">5,000</span>
        </div>
      </div>

      
      <div class="result-box">
        <span style="font-size:14px; font-weight:600; color:#64748b;">4,736</span>
        <span class="arrow-trans">➔</span>
        <span class="res-val" id="res-num">5,000</span>
      </div>
    </div>
  </div>

  <script>
    const modes = [
      {
        targetBox: 'box-t',
        deciderBox: 'box-o',
        deciderVal: 6,
        ruleText: '6 ≥ 5 ➔ Round Up (+1)',
        isUp: true,
        percent: 60,
        lowBound: '4,730',
        highBound: '4,740',
        resText: '4,740'
      },
      {
        targetBox: 'box-h',
        deciderBox: 'box-t',
        deciderVal: 3,
        ruleText: '3 < 5 ➔ Round Down (Stay)',
        isUp: false,
        percent: 36,
        lowBound: '4,700',
        highBound: '4,800',
        resText: '4,700'
      },
      {
        targetBox: 'box-th',
        deciderBox: 'box-h',
        deciderVal: 7,
        ruleText: '7 ≥ 5 ➔ Round Up (+1)',
        isUp: true,
        percent: 73,
        lowBound: '4,000',
        highBound: '5,000',
        resText: '5,000'
      }
    ];

    const boxes = ['box-th', 'box-h', 'box-t', 'box-o'];

    function setMode(index) {
      // Update Tab state
      [0, 1, 2].forEach(i => {
        document.getElementById(`btn-${i}`).classList.toggle('active', i === index);
      });

      const m = modes[index];

      // Clear previous styles
      boxes.forEach(bId => {
        const el = document.getElementById(bId);
        el.classList.remove('target', 'decider');
      });

      // Apply target & decider highlights
      document.getElementById(m.targetBox).classList.add('target');
      document.getElementById(m.deciderBox).classList.add('decider');

      // Update Decision Badge
      const badge = document.getElementById('badge-rule');
      badge.textContent = m.ruleText;
      badge.className = 'decision-badge ' + (m.isUp ? 'up' : 'down');

      // Update Number line track
      document.getElementById('track-prog').style.width = m.percent + '%';
      document.getElementById('track-mark').style.left = m.percent + '%';

      // Update Bounds labels
      const lowEl = document.getElementById('bound-low');
      const highEl = document.getElementById('bound-high');
      lowEl.textContent = m.lowBound;
      highEl.textContent = m.highBound;

      lowEl.classList.toggle('active-bound', !m.isUp);
      highEl.classList.toggle('active-bound', m.isUp);

      // Update Result
      document.getElementById('res-num').textContent = m.resText;
    }

    // Initialize to Nearest 1000 (as in lesson text)
    setMode(2);
  </script>
</body>
</html>

Next time you see any number, just find your target place, look one step to the right, and decide if it rolls down or climbs up!

Under **Curriculum for Excellence** (standard **MNU 3-01a**), the degree of accuracy chosen—whether rounding to the nearest $10$, $100$, or $1000$—must reflect the **context** and required **precision** of the problem.

For example, estimating crowd sizes at a concert works best rounded to the nearest $1000$, while buying supplies for a small class calls for the precision of the nearest $10$.

How do you decide which place value to round to in real-world problems?

Under Curriculum for Excellence standard **MNU 3-01a**, the degree of accuracy chosen (whether rounding to the nearest $10$, $100$, or $1000$) must reflect the **context** and required **precision** of the problem.

For example, estimating the attendance at a huge stadium concert works best rounded to the nearest $1000$, while counting classroom supplies requires the closer precision of the nearest $10$.

math

Rounding Whole Numbers to the Nearest 10, 100, and 1000. Round whole numbers to any given place value using place value rules and number lines.

Examples Rounding to the Nearest 10 and 100

Rounding Whole Numbers to Nearest Ten, Hundred, and Thousand

How to Round Numbers to the Nearest 10, 100 and 1000

Effective instruction for whole number rounding combines visual-spatial models (number lines showing proximity to benchmark multiples) with structured place value analysis. Avoid rote memorisation of isolated rhymes without grounding them in the concept of distance on a number line. Emphasise real-world contexts to connect rounding to estimation and appropriate degrees of accuracy in alignment with Curriculum for Excellence (CfE MNU 3-01a).

Rounding Whole Numbers to the Nearest 10, 100, and 1000

The Number Hill Rule

Rounding to the Nearest 10