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Probability - Business School

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Probability - Business School [#permalink] New post 06 Jun 2011, 20:38
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A certain business school has 500 students, and the law school at the same university has 800 students. Among these students, there are 30 sibling pairs consisting of 1 business student and 1 law student. If 1 student is selected at random from both schools, what is the probability that a sibling pair is selected?

3/40,000
3/20,000
3/4,000
9/400
6/130

In the above Q, what the green color text means? i think it means 2 students (pair) to be selected from the gang since it is mentioned in the red that sibling pair is selected but i just thought that green text is missing 'each'.
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Re: Probability - Business School [#permalink] New post 07 Jun 2011, 01:58
agdimple333 wrote:
A certain business school has 500 students, and the law school at the same university has 800 students. Among these students, there are 30 sibling pairs consisting of 1 business student and 1 law student. If 1 student is selected at random from both schools, what is the probability that a sibling pair is selected?

3/40,000
3/20,000
3/4,000
9/400
6/130

In the above Q, what the green color text means? i think it means 2 students (pair) to be selected from the gang since it is mentioned in the red that sibling pair is selected but i just thought that green text is missing 'each'.


Good point agdimple333:
I prefer the wordings of the following link:
probability-57997.html

The use of word "both" and "pair" indeed creates some ambiguity as to whether we need to choose 2 students from each class OR 1 student from both classes combined.

Let's see using both scenarios:
If 2 students, 1 from each class, need to be selected.
P(Pick Sibling Pair)=(30/500)*(1/800)=30/400000= 3/40000

If just 1 student needs to be selected,
P(Pick from Sibling Pairs)=(30+30)/(500+800)=60/1300=6/130
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Re: Probability - Business School [#permalink] New post 07 Jun 2011, 06:51
thank you and the correct answer is A.
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Re: Probability - Business School [#permalink] New post 11 Jun 2011, 09:10
fluke,

don't you have your definitions reversed? you say 2 students and select only 30 and then you say 1 student and select (30+ 30).
I might be mistaken.

Let's see using both scenarios:
If 2 students, 1 from each class, need to be selected.
P(Pick Sibling Pair)=(30/500)*(1/800)=30/400000= 3/40000

If just 1 student needs to be selected,
P(Pick from Sibling Pairs)=(30+30)/(500+800)=60/1300=6/130
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Re: Probability - Business School [#permalink] New post 11 Jun 2011, 09:28
Hi Puneet,
What Fluke has done is right..
there are 30 pairs of siblings( total 60; 30 in each class)
so selecting one is 500 students is 30/500
now that we have selected 1 sibling - selection of his/her partner is pretty easy
we need to get only that partner out of 30 siblings in 800 students
so its 1/800

together 30/400000 = 3/40000


selecting one student can be done ;

30 pairs = 60 student .
selecting one is 60C1
total 800+500 = 1300
one of 1300 is 1300C1
hence prob= 60c1/1300c1 = 6/130
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Re: Probability - Business School [#permalink] New post 11 Jun 2011, 09:43
thanks Sudhir..got it
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Re: Probability - Business School [#permalink] New post 11 Jun 2011, 11:40
1 student from the both the schools translates to 1 from each school.

agdimple333 wrote:
A certain business school has 500 students, and the law school at the same university has 800 students. Among these students, there are 30 sibling pairs consisting of 1 business student and 1 law student. If 1 student is selected at random from both schools, what is the probability that a sibling pair is selected?

3/40,000
3/20,000
3/4,000
9/400
6/130

In the above Q, what the green color text means? i think it means 2 students (pair) to be selected from the gang since it is mentioned in the red that sibling pair is selected but i just thought that green text is missing 'each'.
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Re: Probability - Business School [#permalink] New post 08 Aug 2011, 13:50
Hi, guys. So what is the right answer?

My method.
I understand the question that we take 1 person from each group.
P(person has a sibling in another group)=30/500
P(2nd group person is sibling)=1/800.

Multiply=30/40 000 or 3/4000

Am I right?
Re: Probability - Business School   [#permalink] 08 Aug 2011, 13:50
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