# Add Fractions with Different Denominators

In this worksheet, students will practice adding fractions with different denominators by finding the lowest common multiple.

Key stage:  KS 2

Curriculum topic:   Number: Fractions, Decimals and Percentages

Difficulty level:

### QUESTION 1 of 10

In this activity, we'll be tackling the topic of adding fractions with different denominators.

What does this yummy looking chocolate cake have to do with fractions?  Let's find out!

Hopefully, we already know that you can't add fractions with different denominators.

denominator tells us how many equal pieces make one whole. If you add the denominators when adding fractions, the new denominator won't describe how many equal pieces are in one whole.

So, we tackle this problem by finding the lowest common multiple to make both denominators the same.

Let's attempt one together:

First, we look at the different denominators and we must find the lowest common multiple of  2 and  i.e.

1 × 2 = 2

2 × 2 = 4

3 × 2 = 6

1 × 3 = 3

2 × 3 = 6

So, we've found our lowest common multiple is 6.

Now, we need to make both our denominators 6.  The key rule to remember here is that whatever you do to the denominator, you must also do to the numerator.

So, if we apply the sums above we end up with:

Pretty simple right?

Now it's over to you. You can always return back to this explanation if you get stuck.

Good luck!

Add these fractions with different denominators.

9/15

9/10

6/10

9/50

Complete the following equation.

9/15

9/10

6/10

9/50

Can you calculate the following?

4/12

3/32

4/32

5/8

Identify the mistake in the working out below.

1/10 + 1/2 = ? [Times 1/2 by 5 to make denominators the same.] The two sum is: 1/10 + 5/10 = 7/10

What is the answer to the sum below?

5/8

7/8

6/32

5/12

Can you find the answer to the sum below?

2/18

3/6

2/9

1/18

Look at this sum.

Zoe has completed the sum, have a look at her working out below.  Unfortunately, something has gone wrong!

Can you spot the error in her working out below?

1/4 + 7/12 = ? [Find the common denominator of 4 and 12.] 1/4 × 4 = 4/16 ...

What do you think the answer is to the sum below?

1/4 + 7/12 = ? [Find the common denominator of 4 and 12.] 1/4 × 4 = 4/16 ...

8/9

7/9

4/9

4/9

Can you answer this final sum?

8/9

7/9

4/9

4/9

• Question 1

Add these fractions with different denominators.

9/10
EDDIE SAYS
How did you get on? The lowest common multiple of both 5 and 10 was already the denominator of the second fraction (10). So, you only needed to times the first fraction by 2 to make both denominators the same. 3/5 × 2 = 6/10 6/10 + 3/10 = 9/10 Don't panic if you struggled with this, we're just getting warmed up. Let's push on!
• Question 2

Complete the following equation.

EDDIE SAYS
First, we need to make the denominators the same. What is the lowest common multiple of 3 and 6? It's 6. 2/3 × 2 = 4/6 4/6 + 1/6 = 5/6 Is this starting to make more sense?
• Question 3

Can you calculate the following?

5/8
EDDIE SAYS
The lowest common multiple of both 4 and 8 is 8. Therefore, we only need to change the denominator of the first fraction. 1/4 x 2 = 2/8 2/8 + 3/8 = 5/8
• Question 4

Identify the mistake in the working out below.

1/10 + 1/2 = ?

[Times 1/2 by 5 to make denominators the same.]

The two sum is:

1/10 + 5/10

= 7/10
EDDIE SAYS
Hopefully, you spotted the silly error the student made right at the end of their working out! 1/10 + 5/10 = 6/10 not 7/10. Make sure to read through your workings out twice to identify any silly mistakes!
• Question 5

What is the answer to the sum below?

7/8
EDDIE SAYS
By this point, you should be starting to feel more confident. The lowest common multiple of 8 and 4 is 8. 2/4 x 2 = 4/8 3/8 + 4/8 = 7/8
• Question 6

Can you find the answer to the sum below?

3/6
EDDIE SAYS
The lowest common multiple of 3 and 6 is 6. 1/3 x 2 = 2/6 1/6 + 2/6 = 3/6 You're making fantastic progress, maths-whiz!
• Question 7

Look at this sum.

Zoe has completed the sum, have a look at her working out below.  Unfortunately, something has gone wrong!

Can you spot the error in her working out below?

1/4 + 7/12 = ?

[Find the common denominator of 4 and 12.]

1/4 × 4 = 4/16 ...
EDDIE SAYS
Did you spot the mistake? The working out should have read: 1/4 + 7/12 = ? 1/4 x 3 = 3/12 3/12 + 7/12 = 10/12 We needed to times 1/4 by 3 to make the denominator 12, not 4!
• Question 8

What do you think the answer is to the sum below?

EDDIE SAYS
How are you getting on? 1/3 + 2/15 = ? This one was a little different. 1/3 = 5/15 5/15 + 2/15 = 7/15
• Question 9

8/9
EDDIE SAYS
2/3 + 2/9 = ? [Find the lowest common multiple of both 3 and 9.] 2/3 × 3 = 6/9 2/9 + 6/9 = 8/9
• Question 10

Can you answer this final sum?

EDDIE SAYS
2/5 + 1/10 = ? [Find the lowest common multiple of 5 and 10.] 2/5 × 2 = 4/10 4/10 + 1/10 = 5/10 Excellent focus maths-whiz! You should now feel super confident when asked to add together two fractions with different denominators. Why not try a more challenging activity and really stretch yourself?
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