bubble-0-to-9Here is an alternative and more unusual version of the “Think of a Number” trick 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.
Subtract 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?

Choose some different pairs of numbers and repeat the process.
Can you discover how the trick works?

Click here for the Notes for Teachers.

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