Decimals are numbers with a fractional part shown after a decimal point. You need to add, subtract, multiply and divide decimals, and round to a given number of decimal places or significant figures.
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Revising decimals the night before an exam? These are condensed revision notes — the facts, formulas and mistakes examiners actually mark, with no long explanations. Prefer a full walkthrough with step-by-step reasoning instead? Search “Decimals GCSE” on the site for the complete guide.
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Key facts to remember
1To add or subtract decimals: line up the decimal points.
2To multiply decimals: ignore the decimal point, multiply as integers, then place the decimal point back.
3To divide by a decimal: multiply both numbers by 10 (or 100 etc.) to make the divisor an integer.
4Rounding to d.p.: look at the (d+1)th digit — if 5 or more, round up; if less than 5, round down.
5Rounding to significant figures: the first significant figure is the first non-zero digit.