law firm

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 144
Joined: Wed Feb 07, 2007 4:13 pm

law firm

by yvonne12 » Tue Apr 10, 2007 3:16 pm
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(2 groups are considered different if least one group members is different)

answer: 100

Senior | Next Rank: 100 Posts
Posts: 46
Joined: Sun Mar 04, 2007 6:27 am

by Tame the CAT » Tue Apr 10, 2007 4:35 pm
4!/3!*6!/(2!4!)+4!/(2!2!)*6!/5!+4!

This gives 100

User avatar
Community Manager
Posts: 789
Joined: Sun Jan 28, 2007 3:51 pm
Location: Silicon valley, California
Thanked: 30 times
Followed by:1 members

by jayhawk2001 » Tue Apr 10, 2007 9:31 pm
S = Senior Partner, J = Junior Partner

Possibilities are SJJ, SSJ and SSS

SJJ = 4C1*6C2 = 60
SSJ = 4C2 * 6C1 = 36
SSS = 4C3 = 4

Sum = 100

Legendary Member
Posts: 559
Joined: Tue Mar 27, 2007 1:29 am
Thanked: 5 times
Followed by:2 members

by Cybermusings » Tue Apr 10, 2007 11:45 pm
Total ways in which 3 partners can be selected from a total of 10 members (6 junior and 4 senior), without restrictions = 10C3 = 120 ways
Total ways in which 3 partners can be selected from a total of 6 junior members (making sure that neither of the 3 chosen are senior partners = 6C3 = 20 ways
Hence groups of 3 partners in which atleast one is a senior partner = 120 - 20 = 100

Master | Next Rank: 500 Posts
Posts: 144
Joined: Wed Feb 07, 2007 4:13 pm

thank you

by yvonne12 » Wed Apr 11, 2007 8:09 am
oh, I didnt add the 3 senior. Although, the question specifically asked for at least 1 senior to be in the group?