With number magic tricks, the magician tells the audience to pick a number and not reveal it. Then, the magician has the audience add, subtract or multiply other numbers to the original number. Thanks to the math involved, the magician can faithfully predict the correct answer every time, making the magician look magical or psychic.
One magic number trick involves the following steps: Pick a three-digit number with the digits in descending order. Reverse those digits to make a second three-digit number and subtract that number from the original number. Reverse the digits of the sum and add the new number to the sum.
The answer, regardless of the number used to start the problem, is 1089. For example, if the audience chooses 643 to start the trick, it would subtract 346 from 643 to get 297. It would then add 792 to 297 to get 1089.
Another number magic trick asks the spectator to choose a number between two and nine, multiply that number by nine, add the digits in the product together and subtract five. Every time the digits of a product of nine are added together, the result is always nine. When five is subtracted, the answer is always four.