This problem is a short challenge that may introduce pupils to the idea of square numbers and square roots. It can also be opened up in all sorts of ways (see the 'Possible extension' section below).

You may want to give learners this challenge as you are taking the register, for example, as it does not need much explanation.

Sharing ways of approaching the solution will be valuable, however, as children are likely to have done different things. Some might have used trial and improvement, some may have used a calculator to find the square root.

Perhaps you could try two consecutive numbers and see how close you are?

Do you have sense of how big the numbers will be?

This problem can be extended in all sorts of ways by asking 'what if ...?' questions. This sheet gives you some suggestions.

A calculator is likely to be useful.