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4 couples wish to stand in a row for a group photo. How many [#permalink]
02 Jan 2008, 09:47

4 couples wish to stand in a row for a group photo. How many arrangements of the 8 people are possible if each person must stand next to his or her partner?

Re: focusing on combinatorics [#permalink]
02 Jan 2008, 10:02

bmwhype2 wrote:

4! 2! 2! 2! 2! = 384

yeah ... it could also be written as 4!*2^4 which means...4! are the positions that all couples may have globally; 2^4 is 2^n and stands for the positions all persons can have in each couple...

can someone explain me the difference with 7-t56557

Re: focusing on combinatorics [#permalink]
02 Jan 2008, 10:21

marcodonzelli wrote:

bmwhype2 wrote:

4! 2! 2! 2! 2! = 384

yeah ... it could also be written as 4!*2^4 which means...4! are the positions that all couples may have globally; 2^4 is 2^n and stands for the positions all persons can have in each couple...

can someone explain me the difference with 7-t56557

there is a sharp difference in the questions. the one i posted is choosing 4 people into a group, in which we want no pairs. In your question, you are simply arranging couples.

_________________

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson

Re: focusing on combinatorics [#permalink]
02 Jan 2008, 10:24

bmwhype2 wrote:

marcodonzelli wrote:

bmwhype2 wrote:

4! 2! 2! 2! 2! = 384

yeah ... it could also be written as 4!*2^4 which means...4! are the positions that all couples may have globally; 2^4 is 2^n and stands for the positions all persons can have in each couple...

can someone explain me the difference with 7-t56557

there is a sharp difference in the questions. the one i posted is choosing 4 people into a group, in which we want no pairs. In your question, you are simply arranging couples.

yeah, I see...but why do we have to divide for 4! in your question? I face this kind of problems in combinatorics...

Re: focusing on combinatorics [#permalink]
03 Jan 2008, 00:58

Expert's post

kazakhb wrote:

I didn't got the point with superscript, how did you come up with 4 in the power?

4P4 - arrangements of 4 couples in a raw 2P2 - arrangements of 2 people in a couple. (2P2)^4 - arrangements of 2 people within a couple for all 4 couples .