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# From a group of 21 astronauts that includes 12 people with

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Manager
Joined: 21 Mar 2007
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From a group of 21 astronauts that includes 12 people with [#permalink]

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01 Jun 2008, 05:52
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Question Stats:

79% (01:08) correct 21% (01:26) wrong based on 166 sessions

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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) 1330
E) 7980

OPEN DISCUSSION OF THIS QUESTION IS HERE: from-a-group-of-21-astronauts-that-includes-12-people-with-136299.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 05 Sep 2013, 01:14, edited 2 times in total.
Topic Moved. Always post the topic in relevant forum

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Manager
Joined: 28 May 2008
Posts: 93

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01 Jun 2008, 06:33
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japped187 wrote:
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) 1330
E) 7980

Hi
The answer is A for me
number of astronauts with previous experience = 12
Remaining =9
we need to pick exactly one from the first group
and 2 from the second group

(12C1)*(9C2)
=12*36= 432

what is the OA?

cheers
!!

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Director
Joined: 03 Sep 2006
Posts: 864

Kudos [?]: 1112 [0], given: 33

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01 Jun 2008, 06:35
japped187 wrote:
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) 1330
E) 7980

$$12*9C2 = 432$$
are "different" combinations possible.

Kudos [?]: 1112 [0], given: 33

Intern
Joined: 16 Aug 2013
Posts: 4

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04 Sep 2013, 22:45
zeenie wrote:
japped187 wrote:
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) 1330
E) 7980

Hi
The answer is A for me
number of astronauts with previous experience = 12
Remaining =9
we need to pick exactly one from the first group
and 2 from the second group

(12C1)*(9C2)
=12*36= 432

what is the OA?

cheers
!!

I have a problem with this question. actually i figure this out in this way (12C1)*(9C2)+(11C1)*(7C2)+(10C1)*(5C2)+(9C1)*(3C2).what i think is after draw 1 from the 12 and 2from the 9, so it is time to drew crews from the 11 and 7.

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MBA Section Director
Status: Back to work...
Affiliations: GMAT Club
Joined: 22 Feb 2012
Posts: 4784

Kudos [?]: 3801 [0], given: 2448

Location: India
City: Pune
GMAT 1: 680 Q49 V34
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04 Sep 2013, 23:06
august31707 wrote:
zeenie wrote:
japped187 wrote:
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) 1330
E) 7980

!!

I have a problem with this question. actually i figure this out in this way (12C1)*(9C2)+(11C1)*(7C2)+(10C1)*(5C2)+(9C1)*(3C2).what i think is after draw 1 from the 12 and 2from the 9, so it is time to drew crews from the 11 and 7.

No, In this case you have to perform two consecutive selections i.e. selection of a experienced astronaut from 12 experienced astronauts AND selection of two inexperienced astronauts from 9 inexperienced astronauts.

selection of a experienced astronaut from 12 experienced astronauts :- 12 C 1

AND ---------------------------------------------------------------------> Multiplication Sign

selection of two inexperienced astronauts from 9 inexperienced astronauts. 9 C 2

In the later event you will choose 2 astronauts from the pool of 9 astronauts simultaneously. Say from the five alphabets a, b, c, d, e you want select a pair of alphabet. Then you will select those alphabets in pairs such as ab, ac, ad, ae, bc, ....... this way.

So (12 C 1) AND (9 C 2) -------> (12 C 1) AND (9 C 2) -------> 432

Hope that Helps!
_________________

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Posts: 42356

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Re: From a group of 21 astronauts that includes 12 people with [#permalink]

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05 Sep 2013, 01:14
japped187 wrote:
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) 1330
E) 7980

$$C^1_{12}*C^2_9=12*36=432$$, where $$C^1_{12}$$ is ways to select 1 astronaut with previous experience out of 12 and $$C^2_9$$ is ways to select 2 astronauts without experience out of 9 remaining astronauts (21-12=9).

OPEN DISCUSSION OF THIS QUESTION IS HERE: from-a-group-of-21-astronauts-that-includes-12-people-with-136299.html
_________________

Kudos [?]: 133195 [0], given: 12439

Re: From a group of 21 astronauts that includes 12 people with   [#permalink] 05 Sep 2013, 01:14
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