Rounding replaces a number with the nearest ten or hundred. Find the deciding digit — the ones digit when rounding to 10, the tens digit when rounding to 100. If it is 5 or more, round up; if it is less than 5, round down. 45 rounds up to 50 because the 5 rounds up, and 43 rounds down to 40 because 3 is under 5. Decide in one step: do not round to 10 first and then to 100.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- round
- replace a number with a nearby simpler one
- deciding digit
- the digit that tells you up or down
Worked examples
Round 45 to the nearest 10
- 1.Deciding digit is 5.
- 2.5 or more rounds up.
= 50
Round 43 to the nearest 10
- 1.Deciding digit is 3.
- 2.Less than 5 rounds down.
= 40
Round 448 to the nearest 100
- 1.Deciding digit (tens) is 4.
- 2.Less than 5 rounds down.
= 400
For parents
Method: Mark the halfway point on a number line and see which side the number falls.
What to say: Ask 'which ten (or hundred) is it nearer to?' and point to the deciding digit.
Common mistakes:
- Rounding a 5 down instead of up (45 to 40).
- Always rounding up (43 to 50).
- Double rounding (448 to 450 to 500).