4 Rules of Fractions

The four rules - adding, subtracting, division and multiplication - with fractions

1. FRACTIONSFRACTIONS
This presentation will help you to:This presentation will help you to:
• addadd
• subtractsubtract
• multiply andmultiply and
• divide fractionsdivide fractions

2. Adding fractionsAdding fractions
To add fractions together the To add fractions together the
denominator denominator (the bottom bit) must be (the bottom bit) must be
the same.the same.
ExampleExample

8
2
8
1

3. Adding fractionsAdding fractions
To add fractions together the To add fractions together the
denominator denominator (the bottom bit) must be (the bottom bit) must be
the same.the same.
ExampleExample

8
2
8
1


8
21

4. Adding fractionsAdding fractions
To add fractions together the To add fractions together the
denominator denominator (the bottom bit) must be (the bottom bit) must be
the same.the same.
ExampleExample

8
2
8
1


8
21
8
3

5. Now try theseNow try these
Click to see the next slide to reveal the answers.Click to see the next slide to reveal the answers.
11. . 22..
33. . 44. .

3
1
3
1

12
7
12
3

7
4
7
2

4
1
4
2

6. Now try theseNow try these
11. . 22..
33. . 44. .

3
1
3
1

12
7
12
3

7
4
7
2

4
1
4
2
3
2
4
3
7
6
12
10

7. Subtracting fractions

8
2
8
3
To subtract fractions the denominator
(the bottom bit) must be the same.
Example

8. Subtracting fractions

8
2
8
3


8
23
To subtract fractions the denominator
(the bottom bit) must be the same.
Example

9. Subtracting fractions

8
2
8
3


8
23
8
1
To subtract fractions the denominator
(the bottom bit) must be the same.
Example

10. Now try these
Click on the next slide to reveal the answers.
1. 2.
3. 4.

3
1
3
2

12
3
12
7

7
3
7
4

4
1
4
2

11. Now try these
.
1. 2.
3. 4.

3
1
3
2

12
3
12
7

7
3
7
4

4
1
4
2
3
1
4
1
7
1
12
4

12. Multiplying fractions
To multiply fractions we multiply
the tops and multiply the bottoms
Top x Top
Bottom x Bottom

13. Multiplying fractions
Example

3
1
2
1

14. Multiplying fractions
Example

3
1
2
1



32
11

15. Multiplying fractions
Example

3
1
2
1



32
11
6
1

16. Now try these
Click on the next slide to reveal the answers.
1. 2.
3. 4.

3
1
3
1

5
3
3
1

5
4
4
2

4
1
4
2

17. Now try these
.
1. 2.
3. 4.

3
1
3
1

5
3
3
1

5
4
4
2

4
1
4
2
9
1
16
2
20
8
15
3

18. Dividing fractions
Once you know a simple trick,
dividing is as easy as multiplying!
• Turn the second fraction upside down
• Change the divide to multiply
• Then multiply!

19. Dividing fractions
•Turn the second fraction upside down
Example ?
3
1
6
1
1
3
6
1


20. Dividing fractions
•Turn the second fraction upside down
Example ?
3
1
6
1
1
3
6
1

•Change the divide into a multiply
1
3
6
1


21. Dividing fractions
•Turn the second fraction upside down
Example ?
3
1
6
1
1
3
6
1

•Change the divide into a multiply
1
3
6
1

•Then multiply 



16
31
1
3
6
1

22. Dividing fractions
•Turn the second fraction upside down
Example ?
3
1
6
1
1
3
6
1

•Change the divide into a multiply
1
3
6
1

•Then multiply 



16
31
1
3
6
1
6
3

23. Now try these
Click on the next screen to reveal the answers.
1. 2.
3. 4.

2
1
3
1

5
4
2
1

6
2
4
1

3
2
4
1

24. Now try these
1. 2.
3. 4.

2
1
3
1

5
4
2
1

6
2
4
1

3
2
4
1
3
2
8
3
8
6
8
5

25. Common denominatorsCommon denominators
To add or subtract fractions together the To add or subtract fractions together the
denominator denominator (the bottom bit) must be (the bottom bit) must be
the same.the same.
So, sometimes we have to change the
bottoms to make them the same.
In “maths-speak” we say we must get
common denominators

26. Common denominatorsCommon denominators
To get a common denominator we have To get a common denominator we have
to:to:
1. Multiply the bottoms together.
2. Then multiply the top bit by the correct
number to get an equivalent fraction

27. Common denominatorsCommon denominators
For example For example
?
3
1
2
1


28. Common denominatorsCommon denominators
For example For example
1.Multiply the bottoms together

?
3
1
2
1

632

29. Common denominatorsCommon denominators
For example For example
?
3
1
2
1

2. Write the two fractions as sixths
6
?
2
1

6
?
3
1


30. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

To get ½ into sixths we have multiplied
the bottom (2) by 3. To get an
equivalent fraction we need to multiply
the top by 3 also

31. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

To get ½ into sixths we have multiplied
the bottom (2) by 3. To get an
equivalent fraction we need to multiply
the top by 3 also
6
3
6
31
2
1




32. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

To get 1/3 into sixths we have multiplied
the bottom (3) by 2. To get an
equivalent fraction we need to multiply
the top by 2 also

33. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

To get 1/3 into sixths we have multiplied
the bottom (3) by 2. To get an
equivalent fraction we need to multiply
the top by 2 also
6
2
6
21
3
1




34. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

We can now rewrite

3
1
2
1

35. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

We can now rewrite
6
2
6
3
3
1
2
1


36. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

We can now rewrite
6
2
6
3
3
1
2
1

6
23


37. Common denominatorsCommon denominators
For example For example

?
3
1
2
1

We can now rewrite
6
2
6
3
3
1
2
1

6
23

6
1


38. Common denominatorsCommon denominators

This is what we have done:
3
1
2
1

1. Multiply the
bottoms
6
?
6
?


39. Common denominatorsCommon denominators

This is what we have done:
3
1
2
1

1. Multiply the
bottoms
6
?
6
?

2.Cross
multiply
6
?
6
31




40. Common denominatorsCommon denominators

This is what we have done:
3
1
2
1

1. Multiply the
bottoms
6
?
6
?

2.Cross
multiply
6
21
6
3

6
?
6
31




41. Common denominatorsCommon denominators

This is what we have done:
3
1
2
1

1. Multiply the
bottoms
6
?
6
?

2.Cross
multiply
6
21
6
3

6
?
6
31



6
2
6
3


42. Now try these
Click on the next slide to reveal the answers.
1. 2.
3. 4.

2
1
3
1

2
1
5
4

6
1
4
3

3
2
4
1
24
14

43. Now try these
.
1. 2.
3. 4.

2
1
3
1

2
1
5
4

6
1
4
3

3
2
4
1
6
5
12
11
24
14
10
3
12
7


44. For further infoFor further info
Go to:Go to:
•BBC Bitesize Maths Revision siteBBC Bitesize Maths Revision site
by clicking here:by clicking here: