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# Fractions - the four rules

## by Steve Bishop, Lecturer at Further education on May 16, 2007

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## Fractions - the four rulesPresentation Transcript

• FRACTIONS
• This presentation will help you to add, subtract, multiply and divide fractions.
Left click on the mouse to reveal the next section
• To learn about: Adding fractions click Subtracting fractions click Dividing fractions click Multiplying fractions click
• Adding fractions
• To add fractions together the denominator (the bottom bit) must be the same.
• Example
• Now try these
• Click on the mouse to reveal the answers.
• 1 . 2 .
• 3 . 4 .
• Subtracting fractions To subtract fractions the denominator (the bottom bit) must be the same. Example
• Now try these Click on the mouse to reveal the answers. 1 . 2 . 3 . 4 .
• Multiplying fractions To multiply fractions we multiply the tops and multiply the bottoms Top x Top Bottom x Bottom
• Multiplying fractions Example
• Now try these Click on the mouse to reveal the answers. 1 . 2 . 3 . 4 .
• 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
• Change the divide into a multiply
• Then multiply
• Now try these Click on the mouse to reveal the answers. 1 . 2 . 3 . 4 .
• 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
• Multiply the bottoms together
• Common denominators
• For example
2. Write the two fractions as sixths
• Common denominators
• For example
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
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
We can now rewrite
• Common denominators This is what we have done: 1. Multiply the bottoms 2.Cross multiply
• Now try these Click on the mouse to reveal the answers. 1 . 2 . 3 . 4 .
• For further info
• Go to:
• BBC Bitesize Maths Revision site
• by clicking here: