Help on combinations problem

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crackgmat007: Legendary Member; Posts: 882; Joined: Fri Feb 20, 2009 2:57 pmFollowed by: 1 member; Thanked: 15 times; GMAT Score:690

by crackgmat007 » Tue Mar 17, 2009 7:34 pm

Help me solve this with steps. Thanks.

In how many arrangements can a teacher seat 3 girls and 3 boys in a row of 6 if the boys are to have the first, third, and fifth seats?
A. 6
B. 9
C. 12
D. 36
E. 720

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Source: Beat The GMAT — Problem Solving | Tue Mar 17, 2009 7:34 pm

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Tue Mar 17, 2009 7:47 pm

Should be 36

First slot: 3 choices (from 3 boys)
2nd :3 choices(3 girls)
3rd slot: 2 choices(2 boys left)
4th slot: 2 choices(2 girls left)
5th slot:1 choice(1 boy left)
6th slot: 1 choice(1 girl left)

3*3*2*2*1*1= 36

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