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Approximation estimates the answer to a calculation by rounding each number to one significant figure, and judges whether an estimate is an over- or under-estimate — a quick way to check a calculation. It's examined right across GCSE and iGCSE Maths. Learn it free on eClassroom through guided worked examples and instantly-marked exam-style questions.
How you do it
Round each number to one significant figure, do the calculation, and state whether your estimate is above or below the true value. If you rounded the top up and the bottom down, your answer is an overestimate.
Before you start
Bring rounding and the four operations with you. This is the foundation for estimating answers and checking calculations.
What you learn
Approximation is about getting a quick, sensible answer — and knowing whether it’s a little too big or too small. It’s the fastest way to check a calculator answer is right. For squares, cubes and roots, round to the nearest square or cube number you know. Sometimes you must say whether your estimate is bigger or smaller than the true answer. The course works through estimating calculations, estimating with squares and roots and over- and under-estimates. 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
Approximation is part of the Number strand of our free GCSE maths courses, studied in Foundation tier. There are 3 teaching sections and 2 fully worked examples, plus 3 sets of check questions. Related topics students usually take next include Compound Growth & Decay, Compound Interest & Decay, Error Intervals, FDP Equivalence and Four Operations. For unlimited practice, the Number revision engine builds new questions on demand and records your accuracy.
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