Round to 1 significant figure, estimate a calculation and say whether it is too big or too small, and use a fact you are given to find related answers.
What you will learn
- Round to 1 significant figure
- Estimate a calculation, including one with a square root
- Say whether an estimate is an overestimate or an underestimate
- Use a given fact such as 47 × 23 = 1081
- Check an answer with an estimate
Estimating a calculation
Round every number to 1 significant figure, then work it out.
For a square root, use the nearest square number instead.
- (6.12 × 38.4) ÷ 0.48
- 6.12 ≈ 6, 38.4 ≈ 40, 0.48 ≈ 0.5
- 6 × 40 = 240
- 240 ÷ 0.5 = 480
- √47.3 × 21.6
- 47.3 is close to 49, so √47.3 ≈ 7
- 21.6 ≈ 20
- 7 × 20 = 140
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Estimating a calculation
- Too big or too small?
- Using a fact you are given
- Checking an answer with an estimate
- Try it: Estimate first, every time
8 practice questions, marked as you go; about 25 minutes in all.
In this unit: Non-calculator methods
Everything Paper 1 asks you to do by hand: written multiplication and division, fractions and percentages, estimating and checking, exact answers, and multi-step problems without a calculator.