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# I took the gmat the other day and one of the few problems

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Intern
Joined: 12 Jul 2007
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I took the gmat the other day and one of the few problems [#permalink]

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21 Sep 2007, 06:22
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

I took the gmat the other day and one of the few problems that I can remember was a combo problem. Probably the reason I can remember it is because I thought i had these simpler combo problems in the bag and of course drew a blank.

Problem goes something like this.

There are 12 books that can be placed in only 5 spaces on a book shelf. How many different combinations of books can there be, order doesn't matter.

Is it 12C5?
= 792?
Senior Manager
Joined: 27 Aug 2007
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21 Sep 2007, 08:29
If you wrote it correctly than,

12!/(7!*5!) = 792,

though it seems to much

cheers
Manager
Status: Post MBA, working in the area of Development Finance
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Re: Combo problem on real gmat [#permalink]

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21 Sep 2007, 08:38
Can we attempt this like:
1st space will be taken by any of the 12 books
2nd space will be taken by any of the 11 books
Thus, 12x11x10x9x8. This is a permutation formula, though!

combres wrote:
I took the gmat the other day and one of the few problems that I can remember was a combo problem. Probably the reason I can remember it is because I thought i had these simpler combo problems in the bag and of course drew a blank.

Problem goes something like this.

There are 12 books that can be placed in only 5 spaces on a book shelf. How many different combinations of books can there be, order doesn't matter.

Is it 12C5?
= 792?
Director
Joined: 15 Jun 2007
Posts: 504
Followers: 1

Kudos [?]: 10 [0], given: 0

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21 Sep 2007, 08:39
Order doesn't matter, so it's a permutation question

12!/7!
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Joined: 21 Jan 2007
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21 Sep 2007, 08:42
shmegs wrote:
Order doesn't matter, so it's a permutation question

12!/7!

order matters in a perm.
Intern
Joined: 12 Jul 2007
Posts: 47
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Kudos [?]: 6 [0], given: 0

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24 Sep 2007, 07:01
I am pretty sure I wrote it correctly. It emphasized that order didn't matter and that the books were chosen from 12 and placed in 5 spaces.

I got a 42 on Q. I think I answered like 3000 something, which I think is wrong.

I got stuck on it because I kept getting huge numbers that weren't in the answers, and I finally just had to pick one and move on.

I guess we still don't have a definitive answer.
24 Sep 2007, 07:01
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