Number · Rounding & bounds
Chapter 1 · 3
The idea
Estimation
Why estimating means rounding everything to 1 significant figure BEFORE calculating, how to divide by decimals cleanly, and how to reason about whether an estimate is an over- or underestimate.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Number · Rounding & bounds
Estimation
Why estimating means rounding everything to 1 significant figure BEFORE calculating, how to divide by decimals cleanly, and how to reason about whether an estimate is an over- or underestimate.
Why it works
Round FIRST, then calculate
An estimate trades precision for speed: round every number to 1 significant figure first, then calculate with the easy numbers. The rounding happens before the arithmetic — that's the whole point, and the whole mark scheme. Calculating exactly and then rounding is a different activity (and on a non-calculator paper, a slow way to lose the method marks).Keep reading — free
The rest of the explanation, plus 2 worked examples you step through move by move.
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