Rounding Rules
- Find the target place you want to round to.
- Look at the digit to its right.
- If that digit is 5 or more → round up. If it is 4 or less → round down (keep the same).
Round 7,348 to the nearest hundred
Target: hundreds digit = 3. Digit to its right: 4 (less than 5).
Round down → 7,300
Round 7,350 to the nearest hundred
Digit to right of hundreds: 5. Round up → 7,400
Rounding Decimals
Same rules apply — just name the decimal place.
Round 3.746 to 1 decimal place
Target: tenths = 7. Next digit: 4 → round down.
Result: 3.7
Estimation
Estimation means finding an approximate answer quickly by rounding first.
Estimate 48 × 31
Round to nearest ten:
(Actual answer: 1488 — very close!)
Always estimate before calculating — it helps you catch big mistakes.
Front-End Estimation
Round each number to its highest place value:
Real world: supermarket shopping estimate
A shopper buys items costing €4.79, €2.15, €8.99, and €1.35. Rounding each: €5 + €2 + €9 + €1 = €17. The till reads €17.28 — the estimate confirmed no item was wrongly scanned. Quick mental rounding is a practical consumer skill.
Real world: engineering tolerances and significant figures
A machinist measures a steel rod as 23.748 mm but must report to 2 decimal places: 23.75 mm. The digit in the third decimal place (4) is less than 5, so they round down to 23.74 mm. Precise rounding prevents parts being machined outside acceptable tolerance.
Real world: scientific data reporting
A chemist measures a liquid volume as 0.004726 L and must round to 2 significant figures: 0.0047 L (the leading zeros are not significant; the first two significant digits are 4 and 7, and the next digit 2 rounds down). Correct rounding ensures experimental data is reported at an appropriate level of precision.
Practice Problems
Round 5,672 to the nearest thousand.
Show answer
Round 0.0348 to 2 decimal places.
Show answer
Estimate: 197 × 41