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# PROBABILITYTANYA.JPG

Author Message
Senior Manager
Joined: 02 Dec 2007
Posts: 426

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27 Sep 2008, 03:23
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PROBABILITYTANYA.JPG [ 58.89 KiB | Viewed 812 times ]

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VP
Joined: 17 Jun 2008
Posts: 1479

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28 Sep 2008, 04:50
1
There are four scenarios - first, second, third or fourth letter goes into the correct envelope.

Now, if first letter goes in correct envelope and other letters goes into incorrect envelope then the probability is
1/4*2/3*1/2*1 = 2/24

Multiply this by 4 for foure different scenarios. Hence, the probability will be 1/3.
VP
Joined: 05 Jul 2008
Posts: 1337

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30 Sep 2008, 18:51
total number of ways to arrange 4 letters in 4 envelopes is 4!

1 correct 3 incorrect

number of ways to pick correct letter and envelope is 4

out of the remaining 3, the first can be placed incorrectly in 2 ways.

the rest two can be placed incorrectly in 1 way

so the probability is 4 * 2 / 24 = 1/3

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: PROBABILITY TANYA   [#permalink] 30 Sep 2008, 18:51
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# PROBABILITYTANYA.JPG

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