Subtracting fractions with the same denominator

Quick answer

To subtract fractions with the same denominator, you simply take away the numerators (the top numbers) and keep the denominator (the bottom number) the same.

Learning outcome

By the end of this page, you will be able to subtract fractions that have the same bottom number, like 5/8 – 2/8, and understand what the answer means in real life.

• You can subtract fractions with the same denominator by taking away the top numbers.
• You know that the bottom number (denominator) stays the same.
• You can explain what your answer means in a real-life situation.
• You can check your answer by adding the result back to the fraction you subtracted from.

Why this matters

Subtracting fractions is useful in everyday life, like when you're sharing a pizza, cutting a cake, or dividing up your lunch. It helps you understand how much is left after you take some away. Whether you're planning a party, cooking a recipe, or playing a game, knowing how to subtract fractions helps you make fair shares and measure what’s left.

For example, if you eat 3 slices of a pizza that was cut into 8 slices, you can work out how many slices are left using subtraction. This skill also helps you in school when you learn more complex fractions, decimals, and percentages later on.

How it works

Subtracting fractions with the same denominator is like taking away parts from a whole. The bottom number (denominator) tells you how many equal parts the whole is split into. The top number (numerator) tells you how many parts you have.

When the denominators are the same, you can just subtract the numerators and keep the denominator the same. Here’s how:

1. Write down the two fractions you are subtracting.
2. Make sure the bottom numbers (denominators) are the same.
3. Subtract the top numbers (numerators).
4. Keep the bottom number (denominator) the same.

For example: 7/10 – 3/10 = 4/10

Examples you can see

Let’s look at some simple examples you can imagine or draw.

Example 1: You have 5/6 of a chocolate bar, and you eat 2/6 of it. How much is left?

• Start with 5/6
• Take away 2/6
• Subtract the numerators: 5 – 2 = 3
• Keep the denominator the same: 6
• Answer: 3/6

Example 2: A cake is cut into 12 pieces. You eat 5 pieces. How many pieces are left?

• You start with 12/12 (the whole cake)
• You eat 5/12
• Subtract numerators: 12 – 5 = 7
• Keep denominator: 12
• Answer: 7/12

Example 3: You have 9/10 of a bag of marbles, and you give 4/10 to your friend. How many marbles do you have left?

• Start with 9/10
• Give away 4/10
• Subtract numerators: 9 – 4 = 5
• Keep denominator: 10
• Answer: 5/10

Try it as a mini adventure

Adventure: The Fraction Bakery

You are a baker in a magical fraction bakery. You have a large tray of 12 cupcakes, and each cupcake is cut into 12 equal pieces. You sell 7 pieces of cupcakes to one customer and 3 pieces to another. How many pieces of cupcakes are left?

1. Start with: 12/12 (the whole tray)
2. Sell 7 pieces: 7/12
3. Sell 3 more pieces: 3/12
4. How many pieces are left? Subtract 7/12 and 3/12 from 12/12.
5. First, add the pieces sold: 7 + 3 = 10 pieces
6. Then subtract: 12/12 – 10/12 = 2/12

Great job! You have 2/12 of the tray left. You can also simplify this to 1/6 if you like. The adventure shows how subtracting fractions helps you manage your bakery inventory.

Common mistakes

• Mistake: Subtracting the denominators too. Why it happens: Some children think they must subtract everything. Fix: Always keep the denominator the same. Only subtract the numerators.
• Mistake: Forgetting to write the denominator in the answer. Why it happens: It’s easy to focus on the top numbers. Fix: Always double-check that the bottom number is in your answer.
• Mistake: Thinking that 1/4 – 1/4 = 0/4. Why it happens: Some children think that 0 is not a valid numerator. Fix: Remember that 0/4 means nothing, which is correct!
• Mistake: Subtracting a bigger number from a smaller one. Why it happens: It’s easy to get confused with the order. Fix: Always make sure the first fraction is larger than the second one, or check your subtraction carefully.

Parent and carer guide

Helping your child with subtracting fractions is simple and fun! Here’s how you can support them in just a few minutes:

1. Ask questions: “If you had 6/8 of a pizza and ate 2/8, how much is left?”
2. Use real-life examples: Use food, toys, or even drawing to show fractions.
3. Check together: After they solve a problem, have them add the answer back to the fraction they subtracted from to check.
4. Keep it light: Don’t pressure them. Make it a game or a story.
5. Be patient: It might take a few tries to get it right, and that’s okay!

Remember, fractions are all about parts of a whole, so use everyday objects to help your child see how they work. You can even draw fractions on paper or use LEGO blocks to show how many parts you’re taking away.

Practice questions

1. What is 8/10 – 3/10? Answer: 5/10
2. Subtract 4/7 from 6/7. Answer: 2/7
3. 11/12 – 5/12 = ? Answer: 6/12
4. 9/15 – 6/15 = ? Answer: 3/15
5. 10/10 – 7/10 = ? Answer: 3/10
6. 5/9 – 2/9 = ? Answer: 3/9
7. 7/11 – 4/11 = ? Answer: 3/11
8. 3/8 – 1/8 = ? Answer: 2/8
9. 12/13 – 8/13 = ? Answer: 4/13
10. 6/10 – 6/10 = ? Answer: 0/10

FAQ

What happens if I subtract a fraction from itself?

When you subtract a fraction from itself, like 5/6 – 5/6, the answer is 0/6, which means nothing is left.

Can I subtract fractions with different denominators?

Yes, but it’s a bit more complex. You need to find a common denominator first. This page focuses on fractions with the same denominator.

Why do we keep the denominator the same?

Because the denominator tells us how many equal parts the whole is divided into. If we're taking away parts from the same whole, the number of parts stays the same.

Can I simplify my answer after subtracting?

Yes! If your answer can be simplified, like 4/10, you can write it as 2/5. Look for common factors in the numerator and denominator.

How can I practice subtracting fractions at home?

You can use food like pizza or cake, draw fraction circles, or play games with fraction cards. Try asking questions like, “If you had 9/10 of a cookie and ate 4/10, how much is left?”