Street fortune-telling surname _ What is a street fortune-telling surname?

How can a fortune teller on the street give a surname without asking you?

The fortune teller will let you choose the range of surnames. For example, he has a piece of paper with about 10 surnames written on it, and then asks you, is your surname on this paper? If not, he will take out another one and repeat it several times. By overlapping mathematics, you can easily identify your surname. If you learn this method, you can do it.