#### 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). |