- Ask a spectator to put a three digit number into the calculator (They have to put the digits in descending order, like 741 or 942).
- Press the subtraction key.
- Then enter the same number in reverse order eg 147 or 249.
- Press the equals key.
- Keep the answer on the display. Remember it and mentally reverse the answer.
- Press the add key.
- Enter the three digit number which you reversed.
- Press the equals sign.
- Your answer will be 1089.
Let's try it:
For example your friend choose the number: 753.
753 - 357 = 396
396 + 693 = 1089
If you really want to impress people, put a piece of paper with 1089 on it in a sealed envelope and open it after the trick!