Significant figures in calculations

2026-11-06Numbers & Estimation Mr Yip

Count significant figures and round answers as papers require.

Key formulas

3 s.f. \text{from the first non}-\text{zero digit}

What this lesson covers

This lesson builds Secondary 2–3 skill in significant figures. Read the key formulas, study the worked example, then attempt the written practice and the four-question MCQ review.

Method

Write every step. Name the rule you use (significant figures) before substituting numbers. Keep units and signs visible until the final sentence.

Common mistakes

Students often rush the sign, use the wrong percentage base, or cancel terms instead of factors. Pause after each line and ask whether the step is reversible.

Exam habit

Underline the question verb (simplify, solve, factorise, find). Box the final answer and, where sensible, substitute back for a quick check.

Worked example

Worked example — significant figures

Problem. Apply the method for significant figures with the numbers 8 and 3.

Solution. Identify the rule for significant figures. Substitute 8 and 3 carefully with signs in brackets if needed. Complete each operation on a new line. State the final answer clearly and check by reversing one step.

Review quiz

1 / 4

Warm-up on significant figures: what is 7+6?

Practice questions

Practice 1 on significant figures: compute with the value 14.
Practice 2 on significant figures: change the numbers and repeat the same method.
Practice 3 on significant figures: write one sentence explaining the key rule.
Practice 4 on significant figures: invent a similar exam-style question and solve it.

Study notes

What is the main idea of significant figures?

Apply the stated formula or rule with clear steps, then check by reversing or substituting.

How should I revise this topic?

Cover the worked example, redo the practice without notes, then complete the MCQ set and log any wrong options.