GCSE — mathsFoundation2 min read

Rounding and Estimation

Round numbers to decimal places and significant figures for GCSE Maths. Use estimation to check calculations.

Tutor AI Team2026-02-25T01:43:30.341Z

Rounding simplifies numbers while keeping them close to the original value. Estimation uses rounded numbers to quickly check whether an answer is reasonable. Both are essential GCSE skills.

Core Concepts

Rounding to Decimal Places (d.p.)

Count digits after the decimal point.

$3.4567$ to 2 d.p. → $3.46$ (look at 3rd decimal: 6 ≥ 5, round up)
$0.0342$ to 1 d.p. → $0.0$ (look at 2nd decimal: 3 < 5, round down)

Rounding to Significant Figures (s.f.)

Count from the first non-zero digit.

$0.00456$ to 2 s.f. → $0.0046$
$3572$ to 2 s.f. → $3600$
$0.07081$ to 3 s.f. → $0.0708$

Estimation

Round each number to 1 s.f. then calculate:

$\frac{19.8 \times 4.1}{0.52} \approx \frac{20 \times 4}{0.5} = \frac{80}{0.5} = 160$

Truncation

Cut off digits without rounding: $3.467$ truncated to 2 d.p. = $3.46$ .

Worked Example: Example 1

Problem

$45,678$ to 3 s.f. = $45,700$

Solution

Worked Example: Example 2

Problem

Estimate $\frac{398 \times 0.48}{21}$

$\approx \frac{400 \times 0.5}{20} = \frac{200}{20} = 10$

Solution

Practice Problems

1. Round 0.005672 to 2 s.f.
1. Estimate $\sqrt{26} \times 3.8$ .
1. Round 4.995 to 2 d.p.

Want to check your answers and get step-by-step solutions?

Key Takeaways

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D.p.: count after the decimal point. S.f.: count from the first non-zero digit.
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5 or above: round up. Below 5: round down.
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Estimation: round to 1 s.f. and calculate — great for checking answers.

Tags:

#gcse#maths#number#rounding#estimation#significant-figures

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