GCSE Maths Revison ; Fractions

8th May 2014

Addition and Subtraction of Factions For GCSE Maths 

The easiest types of fractions to add and subtract are when both bottom numbers (denominators) are the same, e.g. 2/8 + 3/8 = 7/8, or, 4/6 – 2/6 = 2/6.

If the bottom numbers are not the same, they need to be changed by using equivalent fractions, i.e. written in different ways but meaning the same thing.  Remember, lots of equivalent fractions can be made by dividing the top and the bottom by the same number.

If we need to add ½ and 3/8, both of the bottom numbers need to be the same, both can be made to 8 by multiplying, therefore, ½ becomes 4/8 and 3/8 can stay the same , which then gives us

4/8 + 3/8 = 7/8.

It is often necessary to then further cancel down the answer: 8/16 + 4/16 = 12/16 which is ¾ when cancelled down.

Mixed numbers: when adding two vulgar fractions you often get a top heavy answer, e.g.               3/6 + 5/6 =8/6. Top heavy fractions can be simplified to form mixed numbers.

Example: Steve bought 7 bottles of lemonade each containing ¾ pint.  How many pints of lemonade did Steve have?

So, Steve has 7 lots of 3/4, which is 7 x ¾ or 21/4. There are four quarters in a whole so we divide 21 by 4 giving us 5 whole pints with one quarter remaining, therefore, Steve has 5 ¼ pints altogether.

You also need to know how to add two fractions where you need to change both fractions to get the lowest common denominator (get the same bottom number). Take the following sum:

       2/5 + 1/3

Look for the lowest common multiple of 5 & 3 which is 15.

Then, make both fractions into fifteenths:

   2/5 + 1/3 >>>>>> 6/15 + 5/15 =11/15.

Have you listened to the Maths GCSE songs? You can here http://learnthrumusic.co.uk/subjects/#subject-2


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