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# GMAT prep Q5

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Intern
Joined: 21 May 2006
Posts: 45

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19 Jul 2006, 14:14
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi,

Can someone help with this question ?

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VP
Joined: 25 Nov 2004
Posts: 1483

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19 Jul 2006, 16:13
= (60/1000)(1/800) = 3/40,000
Intern
Joined: 11 Jul 2006
Posts: 37
Location: Boston

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19 Jul 2006, 19:08
1
KUDOS
This can be explained as :

There are 60 sibling pairs, probability of picking a senior sibling is 60/1000. Only one out of the junior will make this a sibling pair, the probability of which is 1/800. So the combined probabilty is 60/1000 * 1/800 = 3/40000
SVP
Joined: 30 Mar 2006
Posts: 1728

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20 Jul 2006, 02:01
There are 60 people among 1000 who has a sibling among the 800.

Probability of choosing from group 1 = 60/1000
Now that we have selected one person from group one, that person has only 1 sibling in the second group.
Probability of choosing from group 2 = 1/800

Total = 60/1000 *1/800 = 3/40000
20 Jul 2006, 02:01
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