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# A certain junior class has 1000 students and a certain

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Intern
Joined: 20 Jul 2008
Posts: 24
A certain junior class has 1000 students and a certain [#permalink]

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04 Aug 2008, 07:11
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217. 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. 3/40,000
b. 1/3,600
c. 9/2,000
d. 1/60
e. 1/15
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Joined: 07 Nov 2007
Posts: 1799
Location: New York

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04 Aug 2008, 07:40
haidzz wrote:
217. 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. 3/40,000
b. 1/3,600
c. 9/2,000
d. 1/60
e. 1/15

probability of selecting 60 juninors(sibiling) out of 1000 = 60/1000
probablity of selecting matching sibling out 800 students = 1/800

=60/1000 * 1/800 = 3/40000

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Re: PS: Probability   [#permalink] 04 Aug 2008, 07:40
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