Number 5

2 marks · Easy

Estimate the value of 8.17 × 24.6 by rounding each number to 1 significant figure before multiplying.

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8 × 20 = 160 (±5)

Also accept: 8 × 20 = 160; 160

Common mistakes: Estimate using 8 × 25 = 200; Not rounding to 1 significant figure

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Marking points

M1 · 1 mark · Rounding 8.17 to 8 and 24.6 to 20 (or to other correct 1 s.f. values).

A1 · 1 mark · Correct answer after multiplying rounded numbers: 160. (follow-through)

Worked solution

8.17 rounds to 8 (1 s.f.); 24.6 rounds to 20 (1 s.f.).