Let’s go step by step to estimate each expression. We’re not calculating exactly — we’re rounding numbers to make them easier, then multiplying or dividing.
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1. 4.2 × 5.4
Round 4.2 → 4
Round 5.4 → 5
4 × 5 =
20
Check: Actual is about 4×5.4=21.6 or 4.2×5=21 — so 20 is closest among options (20, 24, 13, 14).
✔ Best estimate:
20
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2. 32.3 ÷ 3.9
Round 32.3 → 32
Round 3.9 → 4
32 ÷ 4 =
8
Check: 3.9 is almost 4, and 32.3 is almost 32 → 8 is perfect.
Actual: 32.3 ÷ 3.9 ≈ 8.28 — so 8 is best.
✔ Best estimate:
8
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3. 8.1 × 3.9
Round 8.1 → 8
Round 3.9 → 4
8 × 4 =
32
Check: Options are 33, 30, 31, 32 → 32 is exact match for our estimate.
Actual: ~8×4=32, slightly less because both rounded up a bit? Wait: 8.1>8, 3.9<4 → might balance. But 32 is still best choice.
✔ Best estimate:
32
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4. 63.7 ÷ 8.1
Round 63.7 → 64
Round 8.1 → 8
64 ÷ 8 =
8
So it’s close to 8.
Actual: 63.7 ÷ 8.1 ≈ 7.86 — which is closer to 8 than to 9.
✔ Best estimate:
Close to 8
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5. 7 × 3.8
3.8 is between 3 and 4.
7 × 3 = 21
7 × 4 = 28
So answer is between 21 and 28 → that’s
between 20 and 30
Options: “Between 10 and 20” or “Between 20 and 30” → clearly second one.
✔ Best estimate:
Between 20 and 30
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Final Answer:
1. 20
2. 8
3. 32
4. Close to 8
5. Between 20 and 30
Parent Tip: Review the logic above to help your child master the concept of estimating decimals worksheet.
