Estimation and checking calculations
Edexcel 1MA1 tests estimation across both tiers, especially Paper 1F and 1H non-calculator sections. The skill is rounding each input to 1 significant figure (1 s.f.), then computing.
Method
- Round each value to 1 s.f.
- Carry out the simpler calculation.
- State the estimate clearly.
- Optionally compare the estimate to the actual answer to spot input errors.
✦Worked example
Estimate 593 × 0.214 ÷ 7.83.
- 593 ≈ 600
- 0.214 ≈ 0.2
- 7.83 ≈ 8
Estimate: 600 × 0.2 ÷ 8 = 120 ÷ 8 = 15.
Actual = 16.207..., so 15 is a good ballpark.
Useful rounding rules
- Numbers ≥ 1: round to first non-zero digit, replacing rest with zeros (593 → 600).
- Numbers < 1: round to first non-zero digit (0.0247 → 0.02).
- Halves traditionally round up (4.5 → 5).
Why estimate?
- To spot calculator key-press errors.
- To "sanity-check" a final answer.
- To do quick calculations when a precise value is unnecessary.
Common Edexcel mark-scheme phrasing
- M1 for at least two values rounded to 1 s.f.
- M1 for the simpler calculation set out.
- A1 for the correct estimate.
- B1 for stating whether the estimate is bigger or smaller than the actual.
⚠Common mistakes— Common errors
- Rounding inconsistently (some to 1 s.f., others to 2 s.f.).
- Rounding 0.214 to 0 instead of 0.2 (forgetting the leading-zero rule).
- Not simplifying enough — defeating the purpose of estimation.
- Computing exactly and calling it an estimate.
AI-generated · claude-opus-4-7 · v3-edexcel-maths-leaves