This activity is about working out the difference of two square numbers.

We use the fact that a² - b² factorises to (a + b) (a - b)

Using this fact, we can work out:

15² - 8² = (15 + 8) × (15 - 8) = 23 × 7 = 161

Being able to find the difference between two squares in this way can sometimes make it possible to do the calculation without the use of a calculator!

Let's have a go at some questions.