The principle of creation is the subtraction of two additions, and a constant solution is obtained by removing the subtraction of the unknown value of the common denominator.

Let the subjects drill a positive integer x, including 0, and let the subjects remember what they chose. Forget it, then multiply X by 2 to get A, then add A to 8 to get B, then divide B by 2 to get C, and subtract the first selected X number from C to get 4. No matter what X you choose, the final answer is 4. Then you can add something casually at the back, and finally tell the answer mysteriously.

The number said by the audience corresponds to an instant. The magician dealt 12 cards. What he remembers is 13. Magic can be performed by guessing cards or two cards. It can be writing a note to predict.