This short challenge presents children with the opportunity of exploring number operations and practising mental arithmetic in a motivating context.

What kind of number is $15$?

How will you remember what you have pressed?

What have you tried so far?

You could challenge children to explain how they would work out, say $24 \times 37$ if a particular number on the calculator was broken. How would they do it if the $2$ was broken? What about if the $1$ and $2$ were broken etc.?

Having calculators to hand will allow learners to check their ideas and they may need to be reminded to record the process in some way.