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# A certain junior class has 1000 students and a certain

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Manager
Joined: 20 Sep 2007
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A certain junior class has 1000 students and a certain [#permalink]  07 Jul 2008, 19:59
A certain junior class has 1000 students and a certain senior class has 800 students. Among these students there are 60 sibling pairs, each consisting of 1 junior and 1 senior . If 1 student is to be selected at random from each class , what is the probability that the 2 students selected will be a sibling pair.

a 3/40000

b 1/3600

c 9/2000

d 1/60

e 1/15

OA TO FOLLOW
Manager
Joined: 05 Jul 2008
Posts: 139
GMAT 1: Q V
GMAT 2: 740 Q51 V38
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Re: Choose siblings Gmat prep question [#permalink]  07 Jul 2008, 20:24
neeraj.kaushal wrote:
A certain junior class has 1000 students and a certain senior class has 800 students. Among these students there are 60 sibling pairs, each consisting of 1 junior and 1 senior . If 1 student is to be selected at random from each class , what is the probability that the 2 students selected will be a sibling pair.

a 3/40000

b 1/3600

c 9/2000

d 1/60

e 1/15

OA TO FOLLOW

A for sure.
The probability you can choose a junior who has siblings is 60/1000.
With a junior chosen, the probability you can choose his sibling in senior class is 1/800.
So the probability is 60/1000*1/800=3/40000 (It's so small!
Director
Joined: 27 May 2008
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Re: Choose siblings Gmat prep question [#permalink]  07 Jul 2008, 20:31
Manager
Joined: 20 Sep 2007
Posts: 107
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Kudos [?]: 32 [0], given: 0

Re: Choose siblings Gmat prep question [#permalink]  08 Jul 2008, 21:31
Thanks guys . OA is A
Re: Choose siblings Gmat prep question   [#permalink] 08 Jul 2008, 21:31
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