Permutations - Order Matters

Oldest

Best Reply

Author

Message

TAGS:

Manager

Joined: 25 May 2009

Posts: 145

Concentration: Finance

Schools: CBS '14 (D), Ross '14 (A), Johnson '14 (M), Owen '14 (A)

GMAT Date: 12-16-2011

Followers: 1

Kudos [?]: 25 [3] , given: 2

Permutations - Order Matters [#permalink]

14 Jun 2009, 12:17

This post received
KUDOS

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.

Founder

Status: On Vacation :-)

Affiliations: UA-1K, SPG-G, HH-D

Joined: 04 Dec 2002

Posts: 10397

Location: United States (WA)

GMAT 1: 750 Q49 V42

GPA: 3.5

WE: Information Technology (Hospitality and Tourism)

Followers: 1363

Kudos [?]: 4186 [0], given: 3119

Re: Permutations - Order Matters [#permalink]

14 Jun 2009, 16:06

Thanks!
I added your post to Walker's Sticky: combination-and-probability-references-56486.html
_________________

Founder of GMAT Club

Just starting out with GMAT? Start here... | Want to know your GMAT Score? Try GMAT Score Estimator
Need GMAT Book Recommendations? Best GMAT Books

Co-author of the GMAT Club tests

Find out what's new at GMAT Club - latest features and updates

Intern

Joined: 25 Oct 2009

Posts: 24

Schools: Wharton, HBS, Stanford

Followers: 0

Kudos [?]: 21 [3] , given: 12

Re: Permutations - Order Matters [#permalink]

25 Oct 2009, 19:34

This post received
KUDOS

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.
_________________

KUDOS if you find it helpful

Intern

Joined: 25 Nov 2009

Posts: 16

Location: San Francisco

Schools: Wharton West eMBA, Haas EW, Haas eMBA

Followers: 0

Kudos [?]: 5 [2] , given: 4

Re: Permutations - Order Matters [#permalink]

03 Jan 2010, 10:06

This post received
KUDOS

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

Re: Permutations - Order Matters [#permalink] 03 Jan 2010, 10:06

	Similar topics	Author	Replies	Last post
Similar Topics:	Order matters or not	damit	3	13 Jul 2004, 13:59
	does order matter?	ceg	1	24 Mar 2005, 08:59
	Assuming order does NOT matter, how many ways can you	WinWinMBA	1	25 May 2005, 15:13
	Permutation?	john2005	5	29 Mar 2006, 20:46
	Probability of a number when order doesn't matter	Dixon	1	06 Apr 2013, 23:24

Permutations - Order Matters

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

Permutations - Order Matters

Permutations - Order Matters

Main navigation

GMAT Resources

Partners

MBA Resources