Addition and subtraction
Adding & subtracting decimals
You add and subtract decimals just like whole numbers — as long as you line up the decimal points so each digit is in the right place.
How to do it
1. Estimate the answer first, so you can check it later. 2. Line up the decimal points (ones under ones, tenths under tenths). 3. Add or subtract each column, carrying or regrouping when needed.
Worked examples
Adding decimals: 9.75 + 13.42
- Estimate first: 10 + 13 = 23.
- Line up the decimal points and add each column, carrying when needed.
Answer: 9.75 + 13.42 = 23.17
Subtracting decimals: 34.29 − 7.41
- Estimate first: 34 − 7 = 27.
- Line up the decimal points and subtract each column, regrouping when needed.
Answer: 34.29 − 7.41 = 26.88
Where you see this in real life
- Adding up prices when shopping, like $7.25 + $15.50.
- Working out how much a plant grew: 5.1 m − 3.9 m.
- Adding gymnastics or diving scores together.
Key words
- Decimal point
- The dot that separates whole numbers from parts of a number.
- Estimate
- A sensible guess of about how big an answer should be.
- Carry
- Moving a ten (or one) into the next column when a column adds to 10 or more.