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# Probability

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Senior Manager
Joined: 05 Oct 2008
Posts: 263

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04 Feb 2009, 10:01
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SVP
Joined: 17 Jun 2008
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04 Feb 2009, 11:36
Favorable outcome:

First letter in the right envelope in 1 way.
Second letter in the wrong envelope in 2 ways.
Third letter in the wrong envelope in 1 way.
Fourth letter in the wrong envelope in 1 way.

Thus, ways in which first letter is in the right envelope and other letters in the wrong envelope = 2

Now, the above can happen for three other letters. Hence, total ways = 2*4 = 8.

Total outcome = 4*3*2 = 24

Hence, probability = 8/24 = 1/3
Re: Probability   [#permalink] 04 Feb 2009, 11:36
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# Probability

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