The number system
Rounding decimal numbers
Rounding makes numbers easier to describe. In Stage 6 you round a number with 2 decimal places to the nearest whole number and to the nearest tenth.
To the nearest whole number
Look at the tenths digit (the first after the decimal point): • 0, 1, 2, 3 or 4 → round DOWN (keep the ones digit). • 5, 6, 7, 8 or 9 → round UP (add 1 to the ones digit).
To the nearest tenth
Look at the hundredths digit (the second after the decimal point): • 0–4 → round down, keep the tenths digit. • 5–9 → round up, add 1 to the tenths digit. Always keep exactly 1 decimal place — even if it is zero. If the tenths digit is 9, it becomes 0 and the ones digit goes up by 1.
Worked examples
Nearest whole number
- Round 2.55 to the nearest whole number.
- The tenths digit is 5, which is 5 or more, so round up.
Answer: 2.55 rounds to 3
Nearest tenth
- Round 6.45 to the nearest tenth.
- The hundredths digit is 5, so round the tenths digit up.
Answer: 6.45 rounds to 6.5
Nearest tenth with a carry
- Round 3.95 to the nearest tenth.
- The hundredths digit 5 rounds the tenths 9 up: it becomes 0 and the ones digit increases.
Answer: 3.95 rounds to 4.0
Where you see this in real life
- Saying Usain Bolt ran 100 m in about 10 seconds instead of 9.63 seconds.
- Rounding a $14.65 book to the nearest dollar ($15).
- Reporting a measurement to the nearest tenth of a metre.
Key words
- Round
- To change a number to a nearby, simpler number.
- Nearest tenth
- The closest number with one decimal place.
- Tenth
- The first place after the decimal point.
- Hundredth
- The second place after the decimal point.