KS2 SATs 2019 — Mathematics Paper 1: Arithmetic

The idea

To find a fraction of an amount, the denominator tells you how many equal parts to split the amount into, so divide by the denominator first. The numerator tells you how many of those parts you need, so multiply by the numerator next. For example, thirds mean divide by 3, then take the number of parts shown.

Adding fractions is different: you can only add pieces that are the same size. If the denominators differ, rewrite both fractions as equivalent fractions with a common denominator, often the lowest common multiple of the two denominators.

Once the denominators match, add the numerators only — the denominator stays the same. If the answer is an improper fraction, you may turn it into a mixed number by dividing the numerator by the denominator.

Worked example

Work out 3⁄8 of 64.

1. Divide by the denominator: 64 ÷ 8 = 8. One eighth of 64 is 8.
2. Multiply by the numerator: 8 × 3 = 24. Three eighths is three of those parts.

Answer: 24

Watch out

• Adding the denominators as well as the numerators when adding fractions.
• Multiplying by the numerator before dividing by the denominator, making the numbers harder.