Arithmetic with Fractions


Multiplication is the ONLY easy process with fractions   (to quote from lessons)

   a   b      =     ab                 numerator
   c      d             cd                denominator

Adding, and subtracting are much harder:


Addition
First decide what units to work in; at worst, multiply the denominators… 

   a b      =    ad + bc      and then do  
   c     d                  cd              cancelling 

Subtraction is almost identical:
   
a   b      =    ad - bc      and then do    
   c      d                cd              cancelling


Division requires an extra move: dividing by 2 is the same as multiplying by 1/2, similarly dividing by 2/3 is the same as multiplying by 3/2, so

    a   ÷  b      =         a   d      =    ad  
    c       d                 c       b            bc



Practise this !

Can you do fractions on your calculator? Good, but learn to do without, because this is one of every examiner’s favourite topics on a non-calculator paper.

So, you dream some up, work out the answer and check it against your calculator.


Go on.....

© David Scoins 2017