Rounding and estimating · Year 5
In Year 5 you learn: rounding to 10,000 and beyond; rounding decimals to whole numbers.
Rounding replaces a number with a simpler one that is close to it, such as 47,386 people becoming about 47,000. We round to make numbers easier to read and to estimate answers quickly, which is also the best way to check a calculator answer is sensible.
Key facts
- Find the digit in the place you are rounding to, then look at the next digit: 5 or more rounds up, 4 or less rounds down.
- Rounding to the nearest 10, 100 or 1,000 keeps the size of the number: 3,682 → 3,700 (nearest 100).
- Decimal places count digits after the point: 3.746 → 3.75 (2 d.p.).
- When a 9 rounds up, carry it on: 2.97 to 1 d.p. is 3.0, not 2.10.
Worked examples
Example 1
Round 3,682 to the nearest 100.
Answer: 3,700
Example 2
A number rounds to 450 to the nearest 10. What is the smallest and largest whole number it could be?
Answer: 445 and 454