When we substitute a number for a letter, we simply replace the letter with the number.

However, we must remember that 4b means 4 x b.

Example

Work out the value of the following expression when a = 0.4

3a - 1

Answer

3a - 1

This means 3 x a - 1

Substitute 0.4 for the letter a:

3 x 0.4 - 1

Multiply first - remember the order of BIDMAS (or BODMAS)

1.2 - 1 = 0.2

It might look complicated, but you'll soon find it becomes second nature. Just work through it one step at a time.

Are you ready for some questions?