Rounding & Estimation
Round numbers and use estimation in calculations
Rounding Numbers
Rounding makes numbers simpler. We round to the nearest 10, 100 or 1 000. Look at the digit to the right of the rounding place: if it is 5 or more, round up; if less than 5, round down.
Example
Rounding Examples
Round 3 467 to the nearest 10: look at ones (7 ≥ 5) → 3 470
Round 3 467 to the nearest 100: look at tens (6 ≥ 5) → 3 500
Round 3 467 to the nearest 1 000: look at hundreds (4 < 5) → 3 000
Estimation
Estimation means finding an answer that is close to the exact answer. We round the numbers first, then calculate. Estimation helps us check if our exact answer is reasonable.
Example
Estimation in Action
Estimate 487 + 315:
Round: 500 + 300 = 800
Exact: 487 + 315 = 802 ✓ (close to 800, so answer is reasonable)
Estimate 72 × 48:
Round: 70 × 50 = 3 500
Exact: 72 × 48 = 3 456 ✓
Note
Remember
Estimation doesn't give the exact answer — it gives a close answer to help us check our work. Always round BEFORE calculating.
Key Vocabulary
RoundingReplacing a number with a simpler nearby number
EstimateA close guess, not the exact answer
ReasonableMakes sense, close to the correct answer
Nearest tenThe closest multiple of 10
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Rounding
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