问一个最最弱智的问题

yiyiying

什么时候用排列P(m,n)，什么时候用组合C(m,n)啊？

困惑ing.

chipmunk

Anything related to sequence (A first or B first), you should use P. That's called 排列. If the sequence doesn't matter, then use C 组合.

usdusaj

先分组， 再排列。