KS2 SATs 2023 — Mathematics Paper 1: Arithmetic

The idea

Decimals follow the same place-value rules as whole numbers. For addition and subtraction, write the numbers so the decimal points line up exactly. Then tenths sit under tenths and hundredths under hundredths. If one number has fewer decimal places, add a zero at the end as a placeholder — 4.9 is the same as 4.90.

To multiply a decimal by a whole number, you can ignore the decimal point at first and multiply the digits as whole numbers. Then put the decimal point back in the same position, so the answer has the same number of decimal places as the decimal you started with.

Estimate first: round the decimals to nearby whole numbers so you know roughly where the decimal point belongs in your answer.

Worked example

Work out 8.24 × 5.

1. Ignore the decimal point for a moment: 824 × 5 = 4,120.
2. 8.24 has two decimal places, so the answer must have two decimal places too.
3. Place the decimal point: 4,120 becomes 41.20, which is written as 41.2.

Answer: 41.2

Watch out

• Lining decimals up from the right-hand end instead of by the decimal point.
• Forgetting the placeholder zero, so 4.9 is treated as 4.09.