GCSE-readyCalculating with decimals
Money, measurements and science results are full of decimals. Here is how to add, subtract, multiply and divide them without a calculator.
Adding and subtracting
12.5 + 3.78 = 12.50 + 3.78 = 16.28
9 − 2.46 = 9.00 − 2.46 = 6.54
Multiplying
0.3 × 0.4: 3 × 4 = 12, two decimal places, so 0.12.
2.4 × 1.3: 24 × 13 = 312, two decimal places, so 3.12.
Multiplying by a number between 0 and 1 makes the answer smaller.
Dividing
Dividing by a decimal: multiply both numbers by 10 (or 100) so you divide by a whole number. The answer does not change.
4.8 ÷ 0.2 = 48 ÷ 2 = 24.
Work out 3.6 × 0.25.
- Without the points: 36 × 25 = 900
- Decimal places in the question: 1 + 2 = 3
- So the answer is 0.900
Answer: 0.9
Add and subtract with the points lined up. To multiply, count decimal places. To divide by a decimal, scale both numbers until you divide by a whole number.
- Not “The answer is more than 45”. That happens when you multiply by a number bigger than 1.
- Not “The answer is less than 0.8”. 45 lots of 0.8 is much more than 0.8.
Try two quick questions
See if it has sunk in. Answers are marked straight away.
2 more questions
Try each one, then tap to check.
Work out 23.6 + 4.87.
Show the answer
Answer: 28.47
Line up the decimal points: 28.47.
Work out 10 − 3.58.
Show the answer
Answer: 6.42
Write 10 as 10.00, then subtract: 6.42.
Check you have got it
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Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.