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Unit 7: Numeracy skills

Fractions

Multiplication of fractions

It may help to understand multiplication if you interpret the ‘x’ sign as ‘of’. So:

1 x 2 means 1 of 2 = 1
-   -   -   -   -
2   5   2   5   5

The calculation involves multiplying both numerators and both denominators then cancelling down. For example:

1 x 2 = 1 x 2 = 2 1 = 1              
-   - ------- --------   -            
2   5   2 x 5   10 5   5              

4 x 2 = 4 x 2 =   8 and   7 x 3 = 7 x 3 = 21          
-   - ------- ------ ----   - --------   ---        
5   3   5 x 3   1 5   1 1   8   11 x 8   88          

When multiplying, you can cancel down during the sum as well as at the final stage – it often makes the calculation easier. Fort example:

3 1 x   3 = 1   x 3 1 = 1 x 1 = 1
-----   ----- ------   ----   -   -   -
  9   8 2   9 3     2   3   2   6

    5 x 6 1 = 5 x 1 =   5            
------- -----   ------   -----          
2 4 4     7   4 x 7   2 8            

Creative Commons License
SMILE - Numeracy skills by Tom Frank, Eric Williams and Clare Wright, University of Birmingham Careers Centre adapted by Marion Kelt Glasgow Caledonian University is licensed under a Creative Commons Attribution 3.0 Unported License.