decimals
Subtracting decimals
Subtract decimal numbers with careful alignment and regrouping.
Quick answer
Subtracting decimals is like subtracting whole numbers, but you must make sure the decimal points are lined up correctly. You can use a place value chart or write the numbers with the decimal points in the same column to help you subtract.Learning outcome
By the end of this page, you will be able to subtract decimal numbers with confidence by aligning the decimal points and using regrouping when needed. Success signs:- You can line up decimal numbers correctly
- You can subtract decimals using column subtraction
- You can check your answer using addition
- You can solve real-life problems involving decimal subtraction
Why this matters
Subtracting decimals is useful in everyday life, such as when you are shopping and need to find out how much change you should get. It also helps in cooking when you need to measure ingredients, or when you are planning a trip and need to calculate distances. In school, you will use this skill in science experiments, money problems, and more.How it works
To subtract decimals, follow these steps:- Write the numbers one above the other, making sure the decimal points are in the same column
- If the numbers have a different number of decimal places, add zeros at the end of the shorter number to make them the same
- Subtract as you would with whole numbers, starting from the right
- If you need to borrow, regroup just like with whole numbers
Examples you can see
Let's look at a few examples to help you understand. Example 1: Simple subtraction We want to subtract 2.5 from 5.7.| 5.7 | - 2.5 | = |
|---|---|---|
| 5.7 | - 2.5 | 3.2 |
| 3.2 | - 1.8 | = |
|---|---|---|
| 3.2 | - 1.8 | 1.4 |
| 2.75 | - 0.30 | = |
|---|---|---|
| 2.75 | - 0.30 | 2.45 |
Try it as a mini adventure
Adventure: The Lemonade Stand You are running a lemonade stand. You start the day with 10.5 litres of lemonade. By noon, you sell 4.2 litres. How much lemonade do you have left? 1st time: Start with 10.5 litres 2nd time: Subtract 4.2 litres 3rd time: Line up the decimal points 4th time: Calculate the difference| 10.5 | - 4.2 | = |
|---|---|---|
| 10.5 | - 4.2 | 6.3 |
| 6.3 | - 2.1 | = |
|---|---|---|
| 6.3 | - 2.1 | 4.2 |
Common mistakes
- Mistake: Not lining up the decimal points correctly
Why it happens: Children often forget to pay attention to the decimal point and write numbers in any column.
Fix: Always write the decimal points in the same column and double-check your alignment. - Mistake: Forgetting to add zeros to make decimal places equal
Why it happens: Children may think it's okay to subtract numbers with different decimal places without making them the same.
Fix: Add zeros at the end of the shorter decimal to match the longer one. - Mistake: Incorrectly regrouping or borrowing
Why it happens: Regrouping can be confusing, especially when dealing with multiple decimal places.
Fix: Use place value charts or draw lines to help keep track of the columns. - Mistake: Forgetting to put the decimal point in the answer
Why it happens: Children may think the decimal point is optional or forget it entirely.
Fix: Always place the decimal point directly below the decimal points in the numbers being subtracted.
Parent and carer guide
Parents and carers can support their child by:- Practising with real-life examples like shopping or cooking
- Using visual aids like place value charts or decimal grids
- Encouraging the child to check their work by adding the result back to the number they subtracted
- Making it fun with games or activities involving decimals
- Reassuring the child that it's okay to make mistakes and that learning from them is part of the process
- Ask your child to explain how they lined up the decimal points
- Encourage them to use a place value chart if they're struggling
- Use everyday situations to practice, such as calculating how much money is left after a purchase
- Remind them to double-check their answer by adding the result to the number they subtracted
Practice questions
- Subtract 1.2 from 4.7
Answer: 3.5 - Subtract 3.4 from 8.9
Answer: 5.5 - Subtract 0.6 from 2.3
Answer: 1.7 - Subtract 1.8 from 5.2
Answer: 3.4 - Subtract 0.35 from 1.75
Answer: 1.40 - Subtract 2.1 from 6.4
Answer: 4.3 - Subtract 4.3 from 9.7
Answer: 5.4 - Subtract 0.8 from 3.1
Answer: 2.3 - Subtract 1.4 from 7.6
Answer: 6.2 - Subtract 0.25 from 5.75
Answer: 5.50
FAQ
What is the most important thing to remember when subtracting decimals?
Always line up the decimal points correctly and make sure both numbers have the same number of decimal places by adding zeros if needed.
Why do we need to add zeros when subtracting decimals?
Adding zeros helps us match the decimal places so that we can subtract each column correctly, just like with whole numbers.
How can I check if my answer is correct?
You can add your answer back to the number you subtracted. If you get the original number, your answer is correct.
What happens if I forget to put the decimal point in my answer?
If you forget the decimal point, your answer will be much larger than it should be. Always double-check that your decimal point is in the right place.
Can I subtract a larger decimal from a smaller one?
Yes, but the result will be a negative number. This is more advanced and usually taught in later years.