1. Think of your age (or any number greater than 9).
2. Multiply by 10.
3. Now pick a number less than or equal to 9.
4. Multiply it by 9.
5. Subtract the two results (step 2 and step 4).
6. Ask for the answer.
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To determine the age (or the number picked),
take the units digit of the answer and add it to the rest of the number.
For example:
| 1. Think of your age (or any number greater than 9). | Let's think of 136. |
| 2. Multiply by 10. | Then we get 1360. |
| 3. Now pick a number less than or equal to 9. | Let's pick 3. |
| 4. Multiply it by 9. | Now we get 27. |
| 5. Subtract the two results (step 2 and step 4). | We get 1360 - 27 = 1333. |
| 6. Ask for the answer. | We are told 1333, so add the units digit (3) to the rest of the number (133) to obtain 136 (the original number). |