Copyright © University of Cambridge. All rights reserved.
Here is an alternative and more unusual version of the "Think of a Number" game which you may have heard of before.
Think of two whole numbers under $10$.
Take one of them and add $1$.
Multiply by $5$.
Add $1$ again.
Double your answer.
Add your second number.
Halve this number and tell me your answer.
From your answer I can work out both your numbers very quickly. How?
Try with different numbers until you see how it works and then you'll be ready to amaze your friends!