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.
Subract 1.
Add your second number.
Add 2.
Double again.
Subtract 8.
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're ready to amaze your friends!