Posted by Peter on 29th April 2009

Mental arithmetic: subtracting from 100

subtract-from-100-1Here is a maths worksheet on using mental arithmetic to subtract from 100. This is probably the type of calculation we do more than any other, especially when working out change from £1.00. There are several processes or ways to do these.

Let’s look at an example: 100 – 47.

One way is to add on 3 to make 50 then 50 to make 100: add the 50 and the 3 to make 53.

Another way is to add 50 to make 97 then count on 3 to make 100.

Watch out for the very common error that children make which is adding 3 to the 7 and adding 60 to the 40 and coming up with the answer 64!

Subtract from 100 (pg 1)

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