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by R.blum
Illustrated by J. SinclairFrom the book MATHEMAGIC
Your friend mentally selects any hour on the face of a clock. After performing some number magic, the clock reveals the hour that he is thinking of!
Materials
A clock or a picture of a clock drawn on a piece of paper
A pencil
Presentation
Ask your friend to think of any hour on the clock without telling you. Explain that you are going to point randomly to different numbers on the clock while he silently counts up to 20. Tell him to start with the hour that he is thinking of and add one every time you point to a number.
Example: He's thinking of 8:00 so he counts
9 when you point to the first number,
10 when you point to the second number,
etc.
When he gets to 20, he should say, "Stop!", and your pencil will be pointing to the hour that he is thinking of!
How to Do It
As your friend is counting up to 20, you are counting, too. The first seven numbers that you point to can be any numbers on the clock. However, the eighth number must be 12. Then go backwards around the clock until your friend tells you to stop.
