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An error interval gives the range a rounded or truncated value could have come from, written as an inequality. This topic finds error intervals for rounded measurements. It's examined right across GCSE and iGCSE Maths. Work through it free on eClassroom, with clear worked examples and instantly-marked questions that build your confidence for the exam.
How you do it
Take half of the place value you rounded to. The lower bound is the value minus that half, the upper bound is the value plus it. Write it as an inequality with the lower bound included and the upper bound excluded.
Before you start
Best tackled after rounding and inequality notation. Higher tier students all cover it. It reappears throughout upper and lower bounds. Filed under Number.
What you learn
A rounded number hides a range of possible true values. The error interval captures that range exactly, using inequalities — and rounding and truncation give different intervals. When a value is rounded, the true value lies within half a unit either side. The same ‘half a unit’ rule applies — you just need the size of the rounding unit. Truncation cuts off — it never rounds up — so its interval is different. The course works through error intervals from rounding, decimal places and significant figures and error intervals from truncation. Every section has instant-feedback practice questions matched to Edexcel iGCSE 4MA1 and the other major GCSE boards, and the course finishes with full exam-style questions you mark yourself.
Related Topics
Error Intervals is a Number topic in the GCSE syllabus, covered here at Higher tier. You work through 3 concepts and 2 worked examples, testing yourself at 3 points. Related topics students usually take next include FDP Equivalence, Four Operations and Fractional & Negative Indices. Endless extra practice on this strand is available on the Number revision engine, which generates a fresh question each time.
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