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example: There are five council members (ABCDE), A and D

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Manager
Joined: 01 Jan 2008
Posts: 221
Schools: Booth, Stern, Haas
example: There are five council members (ABCDE), A and D [#permalink]

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16 Oct 2008, 06:11
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example: There are five council members (ABCDE), A and D cannot sit next to each other. How many different possible seating arrangements are there for the five council members?

Is there any other way to solve it except of next way:
5! - 4!2!=72
SVP
Joined: 29 Aug 2007
Posts: 2457
Re: Combinatorics-one more time [#permalink]

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16 Oct 2008, 07:33
kazakhb wrote:
example: There are five council members (ABCDE), A and D cannot sit next to each other. How many different possible seating arrangements are there for the five council members?

Is there any other way to solve it except of next way:
5! - 4!2!=72

your's is the most easiest way.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

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Manager
Joined: 12 Feb 2008
Posts: 176
Re: Combinatorics-one more time [#permalink]

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16 Oct 2008, 08:12
kazakhb wrote:
example: There are five council members (ABCDE), A and D cannot sit next to each other. How many different possible seating arrangements are there for the five council members?

Is there any other way to solve it except of next way:
5! - 4!2!=72

can you please explain the second part 4!2!

thanks,
SVP
Joined: 29 Aug 2007
Posts: 2457
Re: Combinatorics-one more time [#permalink]

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16 Oct 2008, 09:13
elmagnifico wrote:
kazakhb wrote:
example: There are five council members (ABCDE), A and D cannot sit next to each other. How many different possible seating arrangements are there for the five council members?

Is there any other way to solve it except of next way:
5! - 4!2!=72

can you please explain the second part 4!2!

thanks,

lets suppose A and D as X.
No of ways A and D can be put in X = 2
No of ways X, B, C, and E can be put = 4!
so it is 2 (4!) = 48.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Re: Combinatorics-one more time   [#permalink] 16 Oct 2008, 09:13
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