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# (Please solve this problem!) PS Problem #1:

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Intern
Joined: 23 Jun 2009
Posts: 47

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24 Jul 2009, 12:38
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From a group of 21 astronauts that includes 12 people with previous experience in space flight, a 3-person crew is to be selected so that exactly 1 person in the crew has previous experience in space flight. How many different crews of this type are possible?

A) 432
B) 594
C) 864
D) 1,330
E) 7,980

Thanks;...greatly appreciated.
Current Student
Affiliations: ?
Joined: 20 Jul 2009
Posts: 191
Location: Africa/Europe
Schools: Kellogg; Ross (\$\$); Tuck

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24 Jul 2009, 12:44
you must choose 1 person among the 12 that had already been in space and 2 among the 9 remaining.

so you have 12 X (9 choose 2)
12 X 9!/(2!X7!) = 12 X 9X8/2 = 432

Manager
Joined: 18 Jul 2009
Posts: 167
Location: India
Schools: South Asian B-schools

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25 Jul 2009, 11:36
Out of 21 astronauts => 12 with experience + 9 without experience

A committee of 3 (exactly 1 with experience + 2 inexperienced) => 12C1 x 9C2 => 432
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Bhushan S.
If you like my post....Consider it for Kudos

Re: (Please solve this problem!) PS Problem #1:   [#permalink] 25 Jul 2009, 11:36
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