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GMAT Prep - Probability: Envelops and Letters

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Total Guess

by jscoligan » Mon May 12, 2008 10:04 am
Is the answer 27/256?

If not, what is?
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Re: Total Guess

by netigen » Mon May 12, 2008 10:14 am
I think the answer was 1/3
jscoligan wrote:Is the answer 27/256?

If not, what is?
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by akshatsingh » Mon May 12, 2008 10:41 pm
Four envelopes
[] [] [] []
y x x x

1/4 2/3 1/2 1/1

For the second one 2 wrong ones from 3 right ones can be picked
For the third one 1 wrong one from remaining 2 right ones can be picked
For the fourth one 1 wrong one only is left. so 1/1

there can be 4 different ways of attaining a y.
therefore, 4*(1/4)(2/3)(1/2)(1/1) = 1/3

I hope this is correct..
Aks
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