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Tanya prepared 4 different letters to be sent to 4 different

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Joined: 17 Sep 2017
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Re: Tanya prepared 4 different letters to be sent to 4 different  [#permalink]

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New post 26 Nov 2017, 07:37
Can anyone please tell me why the solution has nothing to do with the given " 4 letters have to be send to 4 dif addresses" information?
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Re: Tanya prepared 4 different letters to be sent to 4 different  [#permalink]

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New post 26 Nov 2017, 10:14
Quote:
I think your confusion might come from not seeing the letter/address as a pair but rather as separate entities.

Yes!! This's exactly what I used to think. But after you boiled it down, I figured it out. and the latter approach seems much more easier for me to understand than the shorter way.
Thank you!
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Tanya prepared 4 different letters to be sent to 4 different  [#permalink]

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New post 26 Nov 2017, 10:50
lichting wrote:
Quote:
I think your confusion might come from not seeing the letter/address as a pair but rather as separate entities.

Yes!! This's exactly what I used to think. But after you boiled it down, I figured it out. and the latter approach seems much more easier for me to understand than the shorter way.
Thank you!


Happy to help. There is also a "handshake" combinatorics question on one of the GMAT prep exams that exploited the pairing concept. You might want to check it out.

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Tanya prepared 4 different letters to be sent to 4 different  [#permalink]

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New post 04 May 2018, 10:03
I think that since there cannot be only one envelope with the wrong letter (if one envelope has a wrong letter, then another one must also have a wrong letter) the number of possible combinations reduces to 12:

A B C D
g g g g
g g x x
g x g x
g x x g
x g g x
x g x g
x x g g
x x x x
g x x x - Only one envelope has the right letter
x g x x - Only one envelope has the right letter
x x g x - Only one envelope has the right letter
x x x g - Only one envelope has the right letter

So out of the 12 possible combinations, only 4 have the right letter in the right envelope. This yields 4/12 = 1/3. :dazed
Tanya prepared 4 different letters to be sent to 4 different &nbs [#permalink] 04 May 2018, 10:03

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