Probability theory came into being in the17th century, initially with the development of insurance, but the demand from gamblers is the source for mathematicians to think about the problems in probability theory.

As early as 1654, a gambler Mailer asked Pascal, a mathematician at that time, a question that puzzled him for a long time: "Two gamblers agreed to bet several games, and whoever wins M games first will win all the bets. But when one of them wins a (a