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# data sufficiency

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Intern
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data sufficiency [#permalink]  03 Jul 2008, 03:43
a total of 9 women and 12 men reside in the 21 apartment that are in a certain apartment building, one person to each apartment. If a pool taker is to select one of the apartments at random, what is the probability that the resident of the apartment selected will be a women who is a student?
1) of the women, 4 are student
2) of the women, 5 are not student
looks easy, but I don't understand why B
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Re: data sufficiency [#permalink]  03 Jul 2008, 04:01
Zaur wrote:
a total of 9 women and 12 men reside in the 21 apartment that are in a certain apartment building, one person to each apartment. If a pool taker is to select one of the apartments at random, what is the probability that the resident of the apartment selected will be a women who is a student?
1) of the women, 4 are student
2) of the women, 5 are not student
looks easy, but I don't understand why B

what is the source of this Q ?
Director
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Re: data sufficiency [#permalink]  03 Jul 2008, 04:02
Seems strange to me too. I’d say St1 and St2 are equivalent – because if 5 women are not students, then, clearly, 9-5=4 are, and vice versa. So it should be D...

May I ask what is the source of this question?
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Re: data sufficiency [#permalink]  03 Jul 2008, 04:14
source? to be honest, I don't know, it is a test book made out on the basis of OG, Kaplan.....
so, no way to understand from where it is
may be it is a mistake....
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Re: data sufficiency [#permalink]  03 Jul 2008, 07:11
I remember seeing this question as an example in the MGMAT online course. I'm pretty sure answer was D.
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Re: data sufficiency [#permalink]  03 Jul 2008, 08:14
Answer is D. I remember this from MGMAT.

1) of the women, 4 are student
2) of the women, 5 are not student

Since we know that there are 21 people, there are 21 choices. Ignore the men.

1) If 9 are women, and 4 are students, there are 4/9 students, or 4/21 that are women and students.
2) If 5 women are not students, then that means the remaining 4 students are women, so 4/21 again.
Re: data sufficiency   [#permalink] 03 Jul 2008, 08:14
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