Rounding to an appropriate degree of accuracy
Edexcel 1MA1 examines this on every paper across both tiers. Foundation focuses on rounding to a stated number of decimal places (d.p.) or significant figures (s.f.); Higher extends to choosing an appropriate accuracy level given the context.
Decimal places (d.p.)
Count digits after the decimal point.
- 3.146 to 2 d.p. → look at the third decimal (6, round up) → 3.15.
- 0.0834 to 3 d.p. → look at the fourth decimal (4, round down) → 0.083.
Significant figures (s.f.)
Start counting from the first non-zero digit.
- 0.00472 to 2 s.f. → 0.0047.
- 593 to 1 s.f. → 600.
- 1842 to 2 s.f. → 1800.
Remember to keep zeros to preserve place value (1842 → 1800, not 18).
Choosing accuracy
In context, round to a degree that suits the data:
- Money: 2 d.p. (£4.50, not £4.4982...).
- Length / measurement: typically 1 d.p. or 3 s.f. unless the question specifies.
- Times in seconds for athletes: 2 d.p. for race times.
- Counts of people: round to a whole number (you cannot have 4.7 people).
Calculator answers
Always quote calculator results to 3 s.f. unless told otherwise. Don't round mid-calculation — keep full precision and round only the final answer.
Common Edexcel mark-scheme phrasing
- B1 for the correctly rounded value.
- A1 for an answer to a stated accuracy.
- "Give your answer correct to 3 significant figures" — A1 only awarded if the rounding is correct.
⚠Common mistakes— Common errors
- Truncating instead of rounding (e.g. 3.149 → 3.14 wrongly; correct: 3.15).
- Counting leading zeros as significant figures (0.00472 has only 3 s.f., not 5).
- Rounding mid-calculation and accumulating error.
- Stating "4 people" when calculation gave 3.2 — round UP for "how many you need" questions, even if 3.2 rounds down to 3 conventionally.
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