What is important to know about Estimation?

To estimate, round every number in the calculation to 1 significant figure.

What is important to know about Estimation?

Use the symbol ≈ (approximately equal to), not =.

What is important to know about Estimation?

Estimates give you a sanity check for calculator answers.

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Number · Foundation & Higher

Estimation

Estimation means rounding every number to 1 significant figure, then doing a quick mental calculation to check that a more complex answer is sensible.

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Key facts to remember

1To estimate, round every number in the calculation to 1 significant figure.
2Use the symbol ≈ (approximately equal to), not =.
3Estimates give you a sanity check for calculator answers.
4For division, estimate numerator and denominator separately first.

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Worked examples

Example 1

Estimate the value of (48.3 × 2.95) / 0.197.

Working

Round each to 1 sf: 48.3 ≈ 50, 2.95 ≈ 3, 0.197 ≈ 0.2
(50 × 3) / 0.2 = 150 / 0.2
150 / 0.2 = 750

Answer≈ 750

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Common mistakes

✗Using more than 1 sf and making arithmetic harder.

✗Rounding 0.197 down to 0 instead of 0.2 — cannot divide by 0.

✗Forgetting to use ≈ instead of =.

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Exam tips

✓Always round every number to 1 sf first.

✓After estimating, compare with a given answer to decide if it is reasonable.

✓Show your rounded values before the final calculation.

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