16 min read

Estimation

Rounding every number in a calculation to 1 significant figure gives a fast, rough check on the real answer.

Quick and Rough, On Purpose

Example 1 — estimating a product

Estimate 48 \times 21 . 1 Round each number to 1 significant figure: 48 \to 50, 21 \to 20 2 Multiply the rounded numbers: 50 \times 20 Answer: \approx 1000 (the exact answer, 1008, is very close)

Example 2 — estimating a more complex calculation

Estimate (203 \times 0.48) \div 9.7 . 1 Round each number to 1 significant figure: 203 \to 200, 0.48 \to 0.5, 9.7 \to 10 2 Calculate with the rounded numbers: (200 \times 0.5) \div 10 = 100 \div 10 Answer: \approx 10 (the exact answer is about 10.05 — the estimate is very close)

Practice

Estimate 62 \times 31 by rounding each number to 1 significant figure first.

Your answer

Quick and Rough, On Purpose

Example 1 — estimating a product

Estimate 48 \times 21 . 1 Round each number to 1 significant figure: 48 \to 50, 21 \to 20 2 Multiply the rounded numbers: 50 \times 20 Answer: \approx 1000 (the exact answer, 1008, is very close)

Example 2 — estimating a more complex calculation

Estimate (203 \times 0.48) \div 9.7 . 1 Round each number to 1 significant figure: 203 \to 200, 0.48 \to 0.5, 9.7 \to 10 2 Calculate with the rounded numbers: (200 \times 0.5) \div 10 = 100 \div 10 Answer: \approx 10 (the exact answer is about 10.05 — the estimate is very close)

Practice

Estimate 62 \times 31 by rounding each number to 1 significant figure first.

Your answer