Unit 20 Section 2 : Adding and Subtracting Fractions
In this section we look at how to add and subtract fractions.
Two fractions can only be added or subtracted if they have the same denominator

For example, it is possible to add 
3 
and 
1 
because both fractions have 5 as the denominator. 
 
5  5 
In this case, we simply add the numerators to find the answer: 
3 
+ 
1 
=  4 
  
5  5  5 
If fractions do not have the same denominator, you need to find equivalent fractions which do

For example, it is not possible to add 
3 
and 
1 
without changing each fraction so that they have the same bottom number. 
 
5  4 
We can use equivalent fractions to rewrite each fraction with 20 as the denominator: 
3 
= 
12 
and 
1 
= 
5 
   
5  20  4  20 
Now we can see that 
3 
+ 
1 
= 
12 
+ 
5 
= 
17 
    
5  4  20  20  20 
Example Questions
Examples of questions involving adding and subtracting fractions are given below.
After each example there are practice questions for you to try.
In each case, work out the what you think the answer is, then click
to see whether you are correct.
Example 1
Practice Questions
Example 2
Practice Questions
Exercises
Work out the answers to the questions below and fill in the boxes. Click on the
button to find out whether you have answered correctly. If you are right
then will appear and you should move on to the next
question. If appears then your answer is wrong. Click
on to clear your original answer and have another go.
If you can't work out the right answer then click on
to see
the answer.
When answering fraction questions, fill in all the boxes before checking your answer, like this:
You have now completed Unit 20 Section 2
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Produced by A.J. Reynolds January 2001