Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 22 May 2015, 09:57

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Combinatorics Summary

Author Message
TAGS:
Intern
Joined: 13 Jan 2012
Posts: 42
Followers: 0

Kudos [?]: 8 [3] , given: 0

Combinatorics Summary [#permalink]  29 Jan 2012, 22:28
3
KUDOS
2
This post was
BOOKMARKED
Am not trashing MGMAT's guides...in fact, I'm a fan. But, I think the combinatorics section could've been written a bit more clearer, coz I remember being able to solve these problems using easier techniques in the past.

http://www.mathsisfun.com/combinatorics ... tions.html

Clear, Crisp & Concise formulas for the 4 categories of problems:

[n is the size of the pool, r is the # of objects we're selecting from the pool]

1) ORDER MATTERS = Y, REPETITIONS = allowed
Formula: n raised to the power r

2) ORDER MATTERS = Y, REPETITIONS = not allowed (nPr)
Formula: n! / (n-r)!

3) ORDER MATTERS = N, REPETITIONS = allowed
Formula: (n+r-1)!/( (r!) (n-1)!)

4) ORDER MATTERS = N, REPETITIONS = not allowed (nCr)
Formula: n! / ( (r!) (n-r)! )

Thought I'd share this for others struggling to remember what you learned years ago...
 Manhattan GMAT Discount Codes Kaplan GMAT Prep Discount Codes GMAT Pill GMAT Discount Codes
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 5536
Location: Pune, India
Followers: 1366

Kudos [?]: 6948 [1] , given: 178

Re: Combinatorics Summary [#permalink]  30 Jan 2012, 01:32
1
KUDOS
Expert's post
fxsunny wrote:
Am not trashing MGMAT's guides...in fact, I'm a fan. But, I think the combinatorics section could've been written a bit more clearer, coz I remember being able to solve these problems using easier techniques in the past.

http://www.mathsisfun.com/combinatorics ... tions.html

Clear, Crisp & Concise formulas for the 4 categories of problems:

[n is the size of the pool, r is the # of objects we're selecting from the pool]

1) ORDER MATTERS = Y, REPETITIONS = allowed
Formula: n raised to the power r

2) ORDER MATTERS = Y, REPETITIONS = not allowed (nPr)
Formula: n! / (n-r)!

3) ORDER MATTERS = N, REPETITIONS = allowed
Formula: (n+r-1)!/( (r!) (n-1)!)

4) ORDER MATTERS = N, REPETITIONS = not allowed (nCr)
Formula: n! / ( (r!) (n-r)! )

Thought I'd share this for others struggling to remember what you learned years ago...

If you are hoping to solve all P&C questions using formulas, you will be disappointed. There are a ton of them. One word in the question changes and your formula becomes useless (though there is a new formula for it then). You need to understand some basic concepts of the topic. That will help you handle most of the questions.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Senior Manager Joined: 23 Mar 2011 Posts: 474 Location: India GPA: 2.5 WE: Operations (Hospitality and Tourism) Followers: 13 Kudos [?]: 138 [0], given: 59 Re: Combinatorics Summary [#permalink] 30 Jan 2012, 01:41 Only the 3rd combination I am finding difficult to explore. Rest was nicely explained in the link, thanks.Karishma, you mention about basics, apart from MGMAT guides and forum discussions, would you have any references for those? Pls advice _________________ "When the going gets tough, the tough gets going!" Bring ON SOME KUDOS MATES+++ ----------------------------- Quant Notes consolidated: consolodited-quant-guides-of-forum-most-helpful-in-preps-151067.html#p1217652 My GMAT journey begins: my-gmat-journey-begins-122251.html All about Richard Ivey: all-about-richard-ivey-148594.html#p1190518 Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 5536 Location: Pune, India Followers: 1366 Kudos [?]: 6948 [0], given: 178 Re: Combinatorics Summary [#permalink] 30 Jan 2012, 01:58 Expert's post sdas wrote: Only the 3rd combination I am finding difficult to explore. Rest was nicely explained in the link, thanks.Karishma, you mention about basics, apart from MGMAT guides and forum discussions, would you have any references for those? Pls advice Veritas has a book dedicated to Combinatorics and Probability. It is one of the most comprehensive sources for GMAT Combinatorics theory and practice questions. Also, for the past few weeks, I have been discussing this topic extensively on my blog: http://www.veritasprep.com/blog/categor ... er-wisdom/ _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Math Expert
Joined: 02 Sep 2009
Posts: 27465
Followers: 4305

Kudos [?]: 42100 [2] , given: 5956

Re: Combinatorics Summary [#permalink]  30 Jan 2012, 02:38
2
KUDOS
Expert's post
1
This post was
BOOKMARKED
sdas wrote:
Only the 3rd combination I am finding difficult to explore. Rest was nicely explained in the link, thanks.Karishma, you mention about basics, apart from MGMAT guides and forum discussions, would you have any references for those? Pls advice

Try Combinatorics chapter of Math Book to have an idea about the staff that is tested on the GMAT: math-combinatorics-87345.html

Also try some questions on combinations to practice:
DS: search.php?search_id=tag&tag_id=31
PS: search.php?search_id=tag&tag_id=52
Hard questions on combinations and probability with detailed solutions: hardest-area-questions-probability-and-combinations-101361.html

In addition, note that usually the GMAT combination/probability questions are fairly straightforward and as practice shows you won't encounter more than 2-3 questions from this field.

Hope it helps.
_________________
Manager
Joined: 02 Feb 2012
Posts: 195
Location: United States
Schools: HBS '18
GPA: 3.08
Followers: 1

Kudos [?]: 3 [0], given: 104

Re: Combinatorics Summary [#permalink]  14 Mar 2012, 15:33
Thank you for posting the combinatorics questions Bunuel, it's something I need to improve
Manager
Joined: 09 Jun 2008
Posts: 111
Concentration: Finance, Strategy
Schools: Chicago (Booth) - Class of 2014
GMAT 1: 680 Q50 V31
GMAT 2: Q V0
Followers: 2

Kudos [?]: 12 [0], given: 46

Re: Combinatorics Summary [#permalink]  21 Mar 2012, 10:35
Thanks for the post..... one of Q areas i need to improve on......
_________________

__________________________________________
Giving kudos is the easiest way to thank someone

Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 4920
Followers: 298

Kudos [?]: 54 [0], given: 0

Re: Combinatorics Summary [#permalink]  18 Aug 2014, 00:04
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).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: Combinatorics Summary   [#permalink] 18 Aug 2014, 00:04
Similar topics Replies Last post
Similar
Topics:
Combinatorics 1 13 Oct 2011, 08:21
Combinatorics 2 21 Oct 2010, 13:10
1 Combinatorics 6 08 Aug 2010, 14:15
2 Combinatorics 4 29 Aug 2009, 22:03
Combinatorics 4 04 Aug 2009, 12:38
Display posts from previous: Sort by