Rounding and estimating · Year 10
In Year 10 you learn: error intervals.
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.).
- Significant figures count from the first non-zero digit: 0.00472 → 0.0047 (2 s.f.); 52,391 → 52,000 (2 s.f.).
- When a 9 rounds up, carry it on: 2.97 to 1 d.p. is 3.0, not 2.10.
- Estimate by rounding every number to 1 significant figure, then calculate.
Worked examples
Example 1
Round 0.04716 to 2 significant figures.
Answer: 0.047