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# letters

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Director
Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 03 Feb 2011
Posts: 920
Followers: 13

Kudos [?]: 313 [0], given: 123

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19 Apr 2011, 05:26
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Question Stats:

50% (00:00) correct 50% (02:01) wrong based on 10 sessions

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hey fluke - I am not able to find any tag that says - "permutation". So pls change the tag if required.

In how many different ways can the letters A, A, B, B, B, C, D, E be arranged if the letter C must be to the right of the letter D?

1,680

2,160

2,520

3,240

3,360

[Reveal] Spoiler:
I dont have the OA for this one. But I believe answer is A. Pls verify the reasoning.

There are 8!/(2!*3!) ways to arrange the letters - A, A, B, B, B, C, D, E. Hence half of these arrangements will have C to the right of D and vice- versa.

Total ways = 8!/(2!*3!) / 2 = 8 * 5040 / 2 * 6 * 2 = 1680. Answer A
Math Forum Moderator
Joined: 20 Dec 2010
Posts: 2021
Followers: 157

Kudos [?]: 1558 [0], given: 376

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19 Apr 2011, 05:42
gmat1220 wrote:
hey fluke - I am not able to find any tag that says - "permutation". So pls change the tag if required.

In how many different ways can the letters A, A, B, B, B, C, D, E be arranged if the letter C must be to the right of the letter D?

1,680

2,160

2,520

3,240

3,360

[Reveal] Spoiler:
I dont have the OA for this one. But I believe answer is A. Pls verify the reasoning.

There are 8!/(2!*3!) ways to arrange the letters - A, A, B, B, B, C, D, E. Hence half of these arrangements will have C to the right of D and vice- versa.

Total ways = 8!/(2!*3!) / 2 = 8 * 5040 / 2 * 6 * 2 = 1680. Answer A

Voila!! Your reasoning is same as Bunuel's and you know what it means!!! You have definitely attained a good level of understanding of permutations and combinations. Good job!!

Discussed here:
probability-q-91460.html
_________________
Director
Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 03 Feb 2011
Posts: 920
Followers: 13

Kudos [?]: 313 [0], given: 123

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19 Apr 2011, 06:08
Thanks fluke ! I love this forum. cheers
Re: letters   [#permalink] 19 Apr 2011, 06:08
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