GCSE Mathematics · Edexcel 1MA1 · Topic N.3

Measures and accuracy

Key points

Round to a given number of decimal places or significant figures; the first non-zero digit is the first significant figure.
Estimate by rounding each number to 1 significant figure, then calculate, e.g. $\frac{48.2 \times 3.9}{0.51} \approx \frac{50 \times 4}{0.5} = 400$ .
Error intervals: a length of 7 cm to the nearest cm satisfies $6.5 \le x < 7.5$ . Truncation of 7.8 to 7 gives $7 \le x < 8$ .
Upper and lower bounds (higher): to get the maximum of $a \div b$ , use the upper bound of $a$ and the lower bound of $b$ .
Unit conversions: 1 m = 100 cm, 1 kg = 1000 g, 1 litre = 1000 cm³. Area and volume conversions use squares and cubes: 1 m² = 10 000 cm², 1 m³ = 1 000 000 cm³.
Time: use 24-hour clock carefully and remember there are 60 minutes in an hour (0.25 h = 15 min).

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Every measurement is rounded, so this sub-topic is about knowing how accurate a number really is: rounding, estimating, error intervals and, at Higher tier, upper and lower bounds. It also covers converting between units, including the…

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