Bounds and error intervals: GCSE Maths revision
A measurement rounded to the nearest 10, unit or decimal place has an error interval from half a unit below to half a unit above.
Error interval
Length 8.3 cm to 1 d.p.
Use lower bounds for a minimum product and a mix of lower/upper for a maximum quotient — think about which combination makes the answer as small or large as possible.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
A mass is 40 kg to the nearest 10 kg. Write the error interval.
7.6 to 1 d.p. Lower bound?
x = 4.2 to 1 d.p. Maximum value of 10 / x?
Common mistakes
- Using ≤ on both ends of the error interval for continuous measures.
- Always multiplying two lower bounds when a maximum is required.
Answers and working
Frequently asked questions
Why is the upper bound not included?
Because 8.35 to 1 d.p. would round to 8.4, not 8.3. Hence < 8.35.
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