Fractions

This presentation will help you to:• add• subtract• multiply and• divide fractions

Adding fractions

To add fractions together the denominator (the bottom bit) must be the same.

Example

=+8

2

8

1

Adding fractions

To add fractions together the denominator (the bottom bit) must be the same.

Example

=+8

2

8

1=

+8

21

Adding fractions

To add fractions together the denominator (the bottom bit) must be the same.

Example

=+8

2

8

1=

+8

21

8

3

Now try these

Click to see the next slide to reveal the answers.

1. 2.

3. 4.

=+3

1

3

1

=+12

7

12

3=+

7

4

7

2

=+4

1

4

2

Now try these

1. 2.

3. 4.

=+3

1

3

1

=+12

7

12

3=+

7

4

7

2

=+4

1

4

2

3

24

3

7

6

12

10

Subtracting fractions

=−8

2

8

3

To subtract fractions the denominator (the bottom bit) must be the same.

Example

Subtracting fractions

=−8

2

8

3=

−8

23

To subtract fractions the denominator (the bottom bit) must be the same.

Example

Subtracting fractions

=−8

2

8

3=

−8

23

8

1

To subtract fractions the denominator (the bottom bit) must be the same.

Example

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

Now try these

.

1. 2.

3. 4.

=−3

1

3

2

=−12

3

12

7=−7

3

7

4

=−4

1

4

2

3

14

1

7

1

12

4

Multiplying fractions

To multiply fractions we multiply the tops and multiply the bottoms

Top x Top

Bottom x Bottom

Multiplying fractions

Example

=×3

1

2

1

Multiplying fractions

Example

=×3

1

2

1=

××

32

11

Multiplying fractions

Example

=×3

1

2

1=

××

32

11

6

1

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

Now try these

.

1. 2.

3. 4.

=×3

1

3

1

=×5

3

3

1=×

5

4

4

2

=×4

1

4

29

116

2

20

8

15

3

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!

Dividing fractions

•Turn the second fraction upside down

Example ?=÷31

61

1

3

6

1÷

Dividing fractions

•Turn the second fraction upside down

Example ?=÷31

61

1

3

6

1÷

•Change the divide into a multiply

1

3

6

1×

Dividing fractions

•Turn the second fraction upside down

Example ?=÷31

61

1

3

6

1÷

•Change the divide into a multiply

1

3

6

1×

•Then multiply =××

=×16

31

1

3

6

1

Dividing fractions

•Turn the second fraction upside down

Example ?=÷31

61

1

3

6

1÷

•Change the divide into a multiply

1

3

6

1×

•Then multiply =××

=×16

31

1

3

6

1

6

3

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

Now try these

1. 2.

3. 4.

=÷2

1

3

1

=÷5

4

2

1=÷

6

2

4

1

=÷3

2

4

1

3

28

3

8

6

8

5

Common denominators

To add or subtract fractions together the denominator (the bottom bit) must be 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

Common denominators

To get a common denominator we have to:

1. Multiply the bottoms together.

2. Then multiply the top bit by the correct number to get an equivalent fraction

Common denominators

For example ?3

1

2

1=−

Common denominators

For example

1. Multiply the bottoms together

?3

1

2

1=−

632 =×

Common denominators

For example ?3

1

2

1=−

2. Write the two fractions as sixths

6

?

2

1=

6

?

3

1=

Common denominators

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

Common denominators

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=

×=

Common denominators

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

Common denominators

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=

×=

Common denominators

For example

?3

1

2

1=−

We can now rewrite

=−3

1

2

1

Common denominators

For example

?3

1

2

1=−

We can now rewrite

6

2

6

3

3

1

2

1−=−

Common denominators

For example

?3

1

2

1=−

We can now rewrite

6

2

6

3

3

1

2

1−=−

6

23−=

Common denominators

For example

?3

1

2

1=−

We can now rewrite

6

2

6

3

3

1

2

1−=−

6

23−=

6

1=

Common denominators

This is what we have done:

3

1

2

1−

1. Multiply the bottoms

6

?

6

?−=

Common denominators

This is what we have done:

3

1

2

1−

1. Multiply the bottoms

6

?

6

?−=

2.Cross multiply

6

?

6

31−

×=

Common 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−

×=

Common 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−=

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

Now try these

1. 2.

3. 4.

=+2

1

3

1

=+2

1

5

4=−

6

1

4

3

=+3

2

4

1

6

512

11

24

1410

3

12

7=

For further info

Go to:• BBC Bitesize Maths Revision site

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