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Permutations - Order Matters

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Permutations - Order Matters [#permalink] New post 14 Jun 2009, 11:17
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I was struggling with when to use the permutation formula and when to use the combination formula in various problems. The definitions of permutations and combinations are are sometimes not clear to beginners. The easiest way that I have found to use the permutation formula is when the question states that order matters. Looking for key words in the sentence like:
*Rank
*Arrange
*Place
*Chose
*Pick
and many others signify that order matters. If order matters then use the permutation formula.

Examples:

*In how many ways can 8 CD’s be arranged on a shelf?

*If a softball league has 10 teams, how many different end of the season rankings are possible? (Assume no ties).

*How many different arrangements can be made using two of the letters of the word TEXAS if no letter is to be used more than once?

* A teacher has 15 students and 5 are to be chosen to give demonstrations. How many different ways can the teacher choose the demonstrators given the following conditions.

*In how many ways can a sorority of 20 members select a president, vice president and treasury, assuming that the same person cannot hold more than one office.

All of these questions are answered using the permutation formula: nPr=\frac{n!}{(n-r)!}

This is something that has helped me, hopefully it helps others.
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Re: Permutations - Order Matters [#permalink] New post 14 Jun 2009, 15:06
Expert's post
Thanks!
I added your post to Walker's Sticky: combination-and-probability-references-56486.html
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Re: Permutations - Order Matters [#permalink] New post 25 Oct 2009, 18:34
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I3igDmsu wrote:
* A teacher has 15 students and 5 are to be chosen to give demonstrations. How many different ways can the teacher choose the demonstrators given the following conditions.


I think that in this example order doesn't matter. Could somebody prove/reject, pls

Thanks in advance.
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Re: Permutations - Order Matters [#permalink] New post 03 Jan 2010, 09:06
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My 2 cents is that this forum is a fantastic way to find resources and hone skills and an awful way to try to gander basic concepts from others' posts. I blundered around not really understanding Permutations and such until reading this link (which certainly came from someone in here who I would give credit to if I could)

http://www.themathpage.com/aPreCalc/per ... ions-2.htm
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Re: Permutations - Order Matters [#permalink] New post 01 Dec 2013, 16:47
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Permutations - Order Matters [#permalink] New post 07 Dec 2013, 05:21
Vyacheslav wrote:
I3igDmsu wrote:
* A teacher has 15 students and 5 are to be chosen to give demonstrations. How many different ways can the teacher choose the demonstrators given the following conditions.


I think that in this example order doesn't matter. Could somebody prove/reject, pls

Thanks in advance.



yes order has no work... only combination is req..
Re: Permutations - Order Matters   [#permalink] 07 Dec 2013, 05:21
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