1. Think of a 3 digit number where all the digits are different.

2. Reverse the digits.

3. Subtract the smaller number from the larger number.

4. Reverse the digits again

5. Add the numbers in steps 3 and 4.

Whatever 3 digit number you choose the answer will always be 1089!.

Here's an example:

1. 643

2. 346

3. 643 - 346 = 297.

4. 792.

5. 297 + 792 = 1089!.