How to answer "Estimate" questions in GCSE Maths
Round every value to 1 significant figure first, then calculate. Exact arithmetic loses every mark.
What it means
In GCSE Maths, "estimate" means round every number in the calculation to 1 significant figure, then calculate the simpler expression. The point is to get an approximate answer using mental arithmetic — not to use a calculator on exact values.
What examiners want
- Show every value rounded to 1 s.f. on a separate line first
- Then perform the calculation with the rounded values
- Give the final estimate without rounding it further
- For "estimate the mean", use class midpoints — same idea, different topic
Worked example
Estimate the value of (596 × 21) ÷ 8.2.
Round to 1 s.f.: 596 ≈ 600, 21 ≈ 20, 8.2 ≈ 8. Calculate: (600 × 20) ÷ 8 = 12,000 ÷ 8 = 1,500. Estimate: 1,500.
Common mistakes
- Calculating with exact values instead of rounding first
- Rounding to 2 or 3 s.f. — the mark scheme demands 1 s.f.
- Failing to show the rounded values explicitly before the calculation
- Rounding the final answer further (e.g. to 2 s.f.) when 1 s.f. is what was used
Marks tip
Most "estimate" questions are 2 or 3 marks. One mark is for the rounding line; one for the calculation; one for the answer.
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