Prep-PS-71

lisalee

A certain law firm consists of 4 senior partners and 6 junior partners.  How many different groups of 3 partners can be formed in which at least one member of the group is a senior partner?  (Two groups are considered different if at least one group member is different.)
(A) 48
(B) 100
(C) 120
(D) 288
(E) 600

worker

团队里至少有一位senior组合=团体所有组合－团体里皆是三位junior的組合

10！/[3!(10-3)!]-6![3!(6-3)!]=100

篮球火

至少有一个senior，一共三种情况，一种就是有一个senior, c41乘以c62=15, 第二种二个senior, c42乘以c61=36, 第三种，三个，c43=4  三种情况相加=100