Adding and subtracting Fractions

1
Adding and subtracting Fractions
There are several ways of adding and subtracting
fractions.
This PowerPoint will show you one of the easiest
methods for you to remember.
4 7
Fraction vocabulary
Most people make the mistake of just adding the
numerators together and the denominators together
without doing anything else

1 4
5 8

6
WRONG!!
12
2
Adding and subtracting Fractions
There are several ways of adding and subtracting
fractions.
This PowerPoint will show you 2 methods.
2
2

1 x 8
8

4 x 5
20



28 32
16
14
8
7
4 x 8
32
2
2
1. To find the denominator of the answer,
multiply the denominators in the question.
2. To find the numerator of the answer, multiply
the top left numerator with the bottom right
denominator, and then
This fraction can now be simplified. To simplify
a fraction we divide the top and the bottom by
the same number. If you can not think of a
number, see if you can divide them by 2.
3. Put the operation, and then
Always look to see if it can be simplified again
4. Multiply the bottom left denominator with the
top right numerator
3
Adding and subtracting Fractions
There are several ways of adding and subtracting
fractions.
This PowerPoint will show you 2 methods.

5 7
1 4


7
5 x 4
20

7 x 1

27 28
7 x 4
28
1. To find the denominator of the answer,
multiply the denominators in the question.
2. To find the numerator of the answer, multiply
the top left numerator with the bottom right
denominator, and then
This, unlike the previous problem, can not be
simplified
3. Put the operation, and then
4. Multiply the bottom left denominator with the
top right numerator
4
Adding and subtracting Fractions
The method is exactly the same when you subtract
fractions except you just have to remember the
sign in step 3.
-
5 7
1 4
-

7
5 x 4
20
-
7 x 1

13 28
7 x 4
28
1. To find the denominator of the answer,
multiply the denominators in the question.
2. To find the numerator of the answer, multiply
the top left numerator with the bottom right
denominator, and then
This can not be simplified
3. Put the operation, and then
4. Multiply the bottom left denominator with the
top right numerator
5
Adding and subtracting Fractions
9 3 11 5
78 55
1
23


55
This is a top heavy fraction. It can be turned
into a mixed number.
2 1 3 8
19 24


Your Turn!
How many times does the denominator go into the
numerator?
2 1 3 5
7 15
-

What is the remainder?
Write the remainder over the denominator
5 3 6 4
2 24
1 12
-


6
Adding and subtracting Fractions
What if we have two mixed number fractions?
We split the problem up into whole numbers and
fractions and solve each one separately.

1 4
5 8

1
3


1
3
1 4
5 8


28 32
1 x 8
8

4 x 5
20


4
4
4 x 8
32
Then it is just a simple case of putting the
answers together
7
Adding and subtracting Fractions

2 5
1 8

2
4
21 40
6
52 32
8

3 4
7 8

7
1
20 32
9
10 16
5 8

Your Turn!
-
6 7
2 5

6
2
16 35
4
-
5 8
1 3

1
0
7 24
1
Hint