排列组合c(5,2)怎么算

1、计算排列组合c(5,2)

=P(5 , 2)/ P(2 , 2)

=5!/ (5 - 2)!/ 2!

=5! /3! /2!

=20/2

=10

2、C(m, n)=P(m, n)/ P(n, n)

P(n, n)= n!

P(m, n)= m!/ (m-n)!