4 Rules of Fractions
44
Fractions This presentation will help you to: • add • subtract • multiply and • divide fractions
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The four rules - adding, subtracting, division and multiplication - with fractions
Transcript of 4 Rules of Fractions
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
by clicking here:
