To play seven games, the first six games should be the result of three wins and three losses. If these two people are A and B, there are three ways for A to win three games in the first three games, and there may be two ways for B to win the last game, so there may be 40 ways.
The calculation method of permutation and combination is as follows:
The arrangement A(n, m)=n×(n- 1). (n-m+ 1)=n！ /(n-m)！ (n is subscript and m is superscript, the same below)
Combination C(n, m)=P(n, m)/P(m, m) =n! /m！ (n-m)！ ;
For example:
A(4，2)=4！ /2! =4*3= 12
C(4，2)=4！ /(2! *2! )=4*3/(2* 1)=6