How to Perform Mathemagic magic tricks with math

This cool trick involves a little math, but you won't believe the results! Sometimes we use materials that require adult supervision... like scissors, so make sure you have friends and family around whenever you do magic tricks. You will need
two sheets of paper and a black marker.
1. Preparation: You'll need to write a prediction on one of the pieces of paper. Write the number 1089 in big numbers and then fold the piece of paper into thirds. Write on the outside: PREDICTION.
2. Performance: Have a spectator pick a three digit number where all 3 digits are different, and write it down on top of the other piece of paper. Now, have them subtract the REVERSE of the number. If the result is negative, just make it positive. And if the result is 99, add a zero to the front to make it 099.
3. Now, have them add the REVERSE of that number. The result will always be 1089. Tell them that even though they could have picked any number you knew all along what their answer would be.
4. Open the prediction and show them you had the EXACT SAME NUMBER!