permutation=order matters= nPr=n!/(n-r)!
combination=order doesn't matter= nCr=n!/(n-r)!r!
!=factorial which means like 6!=6*5*4*3*2*1
Example 1: a two person governing committee has three people trying out. how many ways can they be picked?
3C2=3*2*1/2*1*1=3
Example 2: three people are trying out for president and vice president. how many ways can they be picked?
3P2=3*2*1/1=6
No comments:
Post a Comment