circular permutation

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Deepthi Subbu: Master | Next Rank: 500 Posts; Posts: 298; Joined: Tue Feb 16, 2010 1:09 am; Thanked: 2 times; Followed by:1 members

by Deepthi Subbu » Wed Sep 28, 2011 6:13 am

In how many ways can 5 people from a group of 6 people be seated around a circular table?
(A) 56
(B) 80
(C) 100
(D) 120
(E) 144

Source: Beat The GMAT — Problem Solving | Wed Sep 28, 2011 6:13 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 am; Thanked: 230 times; Followed by:21 members

by shankar.ashwin » Wed Sep 28, 2011 6:16 am

First 5 people can be selected from a group of 6 in 6C5 ways = 6.

5 people can be seated in a circular arrangement in (5-1)! ways.

So 6*4! = 144

E

navami: Legendary Member; Posts: 540; Joined: Sat Dec 20, 2008 7:24 pm; Thanked: 37 times; Followed by:6 members

by navami » Wed Sep 28, 2011 7:39 am

agree ans should be nCr * (r-1)!

This time no looking back!!!
Navami

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