In your iGCSE examinations you will have a calculator available.

So why do you need to learn to do calculations without a calculator. There are several reasons. As well as being a useful life skill in many situations, such as evaluating the overall cost of something or how much change you should receive, being able to mentally calculate can also help us to have an idea of the expected answer from a calculator so that we can quickly identify if the answer received is mistaken. There are many reasons a calculator could give a wrong answer, although the main one is accidentally keying in a wrong number or a wrong arithmetic symbol.

First, let’s remind ourselves of the formal method for doing various arithmetic calculations, and then let’s try exercise 2 on page 74 of the core textbook below:

The answers are below:

Informal methods are also important, so let’s see how quickly we can accurately find the answer in the equations below:

The answers are below: