Rounding Numbers
Rounding means replacing a number with a nearby, simpler number that is close in value. It is used every day for estimating, quick calculations, and reporting figures that do not need to be exact.
The Rounding Rule
- Look at the digit immediately to the right of the rounding place.
- If it is 0–4, round down (keep the rounding digit as it is).
- If it is 5–9, round up (increase the rounding digit by 1).
- Replace all digits to the right of the rounding place with zeros.
Rounding to the Nearest Ten
63 → ones digit is 3 (less than 5) → round down → 60
67 → ones digit is 7 (5 or more) → round up → 70
Rounding to Various Places
| Number | Round to Nearest | Digit to Check | Result |
|---|---|---|---|
| 4,372 | Hundred | Tens digit = 7 (≥5) | 4,400 |
| 4,372 | Thousand | Hundreds digit = 3 (<5) | 4,000 |
| 56,851 | Ten | Ones digit = 1 (<5) | 56,850 |
| 99,950 | Hundred | Tens digit = 5 (≥5) | 100,000 |
Using a Number Line
Find the number on a number line. It will sit between two multiples of the rounding unit. The closer multiple is the rounded value. If exactly halfway, round up.
35 rounded to nearest 10: halfway between 30 and 40 → round up → 40
Rounding Decimals
| Number | Round to | Digit to Check | Result |
|---|---|---|---|
| 3.74 | Nearest whole | Tenths = 7 (≥5) | 4 |
| 3.74 | 1 decimal place | Hundredths = 4 (<5) | 3.7 |
| 2.485 | 2 decimal places | Thousandths = 5 (≥5) | 2.49 |
Estimating with Rounding
389 + 212 ≈ 400 + 200 = 600 (quick estimate)
Key Points
- Identify the rounding place, then look one digit to its right.
- 0–4: round down (the rounding digit stays); 5–9: round up (add 1).
- Replace all digits to the right of the rounding place with zeros.
- Rounding may cause a carry that changes several digits (e.g., 9,950 → 10,000).
- Rounding helps estimate and simplify calculations.
Quick Practice
- Round 4,763 to the nearest hundred.
- Round 58 to the nearest ten.
- Round 2.096 to 2 decimal places.
- Estimate 497 + 312 by rounding each to the nearest hundred.
- Round 999,500 to the nearest thousand.
Summary
Rounding is a controlled simplification: you choose a place, check the next digit to the right, and adjust accordingly. It is the key to estimation, measurement, and data reporting. For decimals the process is identical, just applied to decimal place columns instead of whole-number columns.