“Exploring,” Friend, Aug. 1976, 33
Exploring
Fun with Figures
By Trevor Holloway
Tell one of your friends that if he works out a sum in his head you will be able to read his thoughts and tell him the correct answer.
Ask the person to think of a number, double it, and add 20 (or any even number) to it. Then divide the answer by 2 and subtract the original number from it. Now you can tell him the answer he figured in his mind.
The secret is that the answer will always be half of the number you tell your friend to add. Here is an example:
|
Think of a number |
12 |
|
Double it |
24 |
|
Add 40 |
64 |
|
Divide by 2 |
32 |
|
Take away number first thought of (12) |
20 |