The number system
Rounding decimals
Rounding changes a number to the nearest whole number. It makes numbers easier to describe and understand.
The rounding rule
Look at the tenths digit (the first digit after the decimal point): • If it is 0, 1, 2, 3 or 4 → round DOWN. • If it is 5, 6, 7, 8 or 9 → round UP.
Worked examples
Rounding up: 3.9
- Look at the tenths digit: 9.
- 9 is 5 or more, so round up.
Answer: 3.9 rounds to 4
Rounding down: 7.3
- Look at the tenths digit: 3.
- 3 is 4 or less, so round down.
Answer: 7.3 rounds to 7
The halfway case: 4.5
- Look at the tenths digit: 5.
- A tenths digit of 5 always rounds up.
Answer: 4.5 rounds to 5
Where you see this in real life
- Saying an elephant is 'about 3 metres' tall instead of 3.3 metres.
- Rounding a price to the nearest dollar.
- Reporting a measurement to the nearest whole centimetre.
Key words
- Round
- To change a number to a nearby, simpler number.
- Nearest whole number
- The closest whole number to the given number.
- Tenth
- The first place after the decimal point — one part out of ten.