Last visit was: 09 Jun 2026, 21:54 It is currently 09 Jun 2026, 21:54
Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
User avatar
walker
Joined: 17 Nov 2007
Last visit: 25 May 2025
Posts: 2,396
Own Kudos:
Given Kudos: 362
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Expert
Expert reply
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Posts: 2,396
Kudos: 10,883
 [484]
100
Kudos
Add Kudos
383
Bookmarks
Bookmark this Post
Most Helpful Reply
User avatar
shrouded1
User avatar
Retired Moderator
Joined: 02 Sep 2010
Last visit: 29 Apr 2018
Posts: 608
Own Kudos:
3,242
 [197]
Given Kudos: 25
Location: London
Products:
Posts: 608
Kudos: 3,242
 [197]
83
Kudos
Add Kudos
113
Bookmarks
Bookmark this Post
General Discussion
User avatar
gmatdelhi
Joined: 23 Oct 2009
Last visit: 07 Nov 2011
Posts: 58
Own Kudos:
31
 [4]
Given Kudos: 76
Location: New Delhi, India
Schools:Chicago Booth, Harvard, LBS, INSEAD, Columbia
Posts: 58
Kudos: 31
 [4]
Kudos
Add Kudos
4
Bookmarks
Bookmark this Post
avatar
AlyoshaKaramazov
Joined: 25 Jun 2012
Last visit: 10 Jul 2015
Posts: 27
Own Kudos:
71
 [4]
Given Kudos: 4
Posts: 27
Kudos: 71
 [4]
1
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
just wanted to throw these videos from khan academy out there, super helpful in dumbing down the concepts and holding your hand through it

combinations:

https://www.khanacademy.org/math/probabi ... inations_1

permutations:

https://www.khanacademy.org/math/probabi ... utations_1

These should be required watching, MGMAT does a thorough job of confusing my ass in this area.
avatar
santosh18
Joined: 16 Mar 2010
Last visit: 02 Apr 2012
Posts: 6
Own Kudos:
6
 [2]
Given Kudos: 3
Posts: 6
Kudos: 6
 [2]
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
Waiting for the updates..... You hit the nail on the head

"Should I apply C- or P- formula here?". Don't fall in this trap: define how you are going to count arrangements first, realize that your way is right and you don't miss something important, and only then use C- or P- formula if you need them
avatar
ajay0076
Joined: 23 Aug 2010
Last visit: 18 Apr 2011
Posts: 1
Own Kudos:
2
 [2]
Posts: 1
Kudos: 2
 [2]
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
Hi ,

I am just confused when to use permutation and when to use combination formula while solving problems. i mean what is the basic difference between Permutation and combination.
User avatar
gurpreetsingh
Joined: 12 Oct 2009
Last visit: 15 Jun 2019
Posts: 2,266
Own Kudos:
3,976
 [2]
Given Kudos: 235
Status:<strong>Nothing comes easy: neither do I want.</strong>
Location: Malaysia
Concentration: Technology, Entrepreneurship
Schools: ISB '15 (M)
GMAT 1: 670 Q49 V31
GMAT 2: 710 Q50 V35
Products:
Schools: ISB '15 (M)
GMAT 2: 710 Q50 V35
Posts: 2,266
Kudos: 3,976
 [2]
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
nice one shrouded.

I actually do the reverse. I use \(P = A^a * B^b * C^c\) for all the combination problems.

eg....for n identical, P is of the form = a*a* .........n times where a is prime number

so number of ways of selecting n identical -> n+1 using the formula of number of divisors.[ (a+1)*(b+1)*(c+1)]

for n non-identical P is of the form = a*b*c*...........n times

so number of ways of selecting n non-identical -> (1+1)*(1+1)...n times using the formula of number of divisors.

= 2^n

similarly if the number of identical balls are given then take \(P = A^a * B^b * C^c\) where a,b,and c are the number of identical balls of type A,B,and C respectively.

Then use the number of divisor formula = \((a+1)*(b+1)*(c+1)\)
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 09 Jun 2026
Posts: 111,171
Own Kudos:
819,806
 [2]
Given Kudos: 106,735
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 111,171
Kudos: 819,806
 [2]
Kudos
Add Kudos
2
Bookmarks
Bookmark this Post
russ9
walker


Combination

A combination is an unordered collection of k objects taken from a set of n distinct objects. The number of ways how we can choose k objects out of n distinct objects is denoted as:

\(C^n_k\)

knowing how to find the number of arrangements of n distinct objects we can easily find formula for combination:

1. The total number of arrangements of n distinct objects is n!
2. Now we have to exclude all arrangements of k objects (k!) and remaining (n-k) objects ((n-k)!) as the order of chosen k objects and remained (n-k) objects doesn't matter.

\(C^n_k = \frac{n!}{k!(n-k)!}\)



Permutation

A permutation is an ordered collection of k objects taken from a set of n distinct objects. The number of ways how we can choose k objects out of n distinct objects is denoted as:

\(P^n_k\)

knowing how to find the number of arrangements of n distinct objects we can easily find formula for combination:

1. The total number of arrangements of n distinct objects is n!
2. Now we have to exclude all arrangements of remaining (n-k) objects ((n-k)!) as the order of remained (n-k) objects doesn't matter.

\(P^n_k = \frac{n!}{(n-k)!}\)

If we exclude order of chosen objects from permutation formula, we will get combination formula:

\(\frac{P^n_k}{k!} = C^n_k\)


Hello friends - this page seems to be the best find yet. I've been using Manhattan gmat books and their content on Combinatorics and Probability is pretty lacking so please excuse my rudimentary questions.

One topic that i'm having a very hard time grasping is the "ordered vs. unordered" set. Seems like Permutation is ordered and Combination is unordered. I have absolutely no clue what that means and more importantly, I can't connect the dots to figure out why it affects the equations the way it does?

Any help would be appreciated.

In how many way we can choose two letters out of {a, b, c}, of the order of the letters does not matter?

{a, b}
{a, c}
{b, c}

So, in 3 ways: \(C^2_3=3\).

In how many way we can choose two letters out of {a, b, c}, of the order of the letters matters?

{a, b}
{b, a}
{a, c}
{c, a}
{b, c}
{c, b}

So, in 6 ways: \(P^2_3=6\).

I'd advice to go through easier questions on the topic to understand better. Check here: ds-question-directory-by-topic-difficulty-128728.html and here: gmat-ps-question-directory-by-topic-difficulty-127957.html

Hope it helps.
User avatar
MSoS
Joined: 10 Jan 2010
Last visit: 26 Oct 2017
Posts: 108
Own Kudos:
59
 [1]
Given Kudos: 7
Location: Germany
Concentration: Strategy, General Management
Schools: IE '15 (M)
GPA: 3
WE:Consulting (Telecommunications)
Schools: IE '15 (M)
Posts: 108
Kudos: 59
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Thank you for the posted information....much appreciated!!
avatar
Himanshiyadavv
Joined: 24 May 2011
Last visit: 09 Sep 2011
Posts: 3
Own Kudos:
1
 [1]
Posts: 3
Kudos: 1
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
Kudos ... gr8 work... helped me alot in understanding the conce3pts of combinatorics.. as i m always confused with them... thnks for the notes...
User avatar
SonyGmat
Joined: 23 Oct 2011
Last visit: 22 Mar 2012
Posts: 55
Own Kudos:
605
 [1]
Given Kudos: 34
Posts: 55
Kudos: 605
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
walker

Combination

A combination is an unordered collection of k objects taken from a set of n distinct objects. The number of ways how we can choose k objects out of n distinct objects is denoted as:

\(C^n_k\)

knowing how to find the number of arrangements of n distinct objects we can easily find formula for combination:

1. The total number of arrangements of n distinct objects is n!
2. Now we have to exclude all arrangements of k objects (k!) and remaining (n-k) objects ((n-k)!) as the order of chosen k objects and remained (n-k) objects doesn't matter.

\(C^n_k = \frac{n!}{k!(n-k)!}\)



Permutation

A permutation is an ordered collection of k objects taken from a set of n distinct objects. The number of ways how we can choose k objects out of n distinct objects is denoted as:

\(P^n_k\)

knowing how to find the number of arrangements of n distinct objects we can easily find formula for combination:

1. The total number of arrangements of n distinct objects is n!
2. Now we have to exclude all arrangements of remaining (n-k) objects ((n-k)!) as the order of remained (n-k) objects doesn't matter.

\(P^n_k = \frac{n!}{(n-k)!}\)

If we exclude order of chosen objects from permutation formula, we will get combination formula:

\(\frac{P^n_k}{k!} = C^n_k\)

Great Post.

I believe that the formulas can be used only when \(N\geq K\)
User avatar
catty2004
Joined: 30 May 2008
Last visit: 01 Nov 2016
Posts: 33
Own Kudos:
997
 [1]
Given Kudos: 26
Posts: 33
Kudos: 997
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
walker
The topic is not finished.

COMBINATORICS

created by: walker
edited by: bb, Bunuel

--------------------------------------------------------

This post is a part of [GMAT MATH BOOK]



--------------------------------------------------------

Circular arrangements

Let's say we have 6 distinct objects, how many relatively different arrangements do we have if those objects should be placed in a circle.



The difference between placement in a row and that in a circle is following: if we shift all object by one position, we will get different arrangement in a row but the same relative arrangement in a circle. So, for the number of circular arrangements of n objects we have:
\(R = \frac{n!}{n} = (n-1)!\)

Tips and Tricks

Any problem in Combinatorics is a counting problem. Therefore, a key to solution is a way how to count the number of arrangements. It sounds obvious but a lot of people begin approaching to a problem with thoughts like "Should I apply C- or P- formula here?". Don't fall in this trap: define how you are going to count arrangements first, realize that your way is right and you don't miss something important, and only then use C- or P- formula if you need them.


Resources

Walker's post with Combinatorics/probability problems: [Combinatorics/probability Problems]

--------------------------------------------------------

Attachment:
Math_Combinatorics_6balls.png
Attachment:
Math_Combinatorics_6balls_b.png
Attachment:
Math_Combinatorics_6balls_l.png
Attachment:
Math_Comb_Round_t.png


having a hard time understand the formula under circular arrangement :(
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 09 Jun 2026
Posts: 111,171
Own Kudos:
819,806
 [1]
Given Kudos: 106,735
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 111,171
Kudos: 819,806
 [1]
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
AA2014
can u please share something like this on "Probability" as well?????

Check here: math-probability-87244.html
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 09 Jun 2026
Posts: 111,171
Own Kudos:
819,806
 [1]
Given Kudos: 106,735
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 111,171
Kudos: 819,806
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
kuvshah
Circular arrangements having hard time understanding how did you arrive at the formula of dividing n! by n. Can someone please elaborate?

Thanks
Kunal

The number of arrangements of n distinct objects in a row is given by \(n!\).
The number of arrangements of n distinct objects in a circle is given by \((n-1)!\).

The difference between placement in a row and that in a circle is following: if we shift all object by one position, we will get different arrangement in a row but the same relative arrangement in a circle. So, for the number of circular arrangements of n objects we have:

\(\frac{n!}{n} = (n-1)!\).

Check other Arrangements in a Row and around a Table questions in our Special Questions Directory.
User avatar
g4gmat
Joined: 15 Dec 2009
Last visit: 05 Dec 2011
Posts: 9
Own Kudos:
23
 [1]
Given Kudos: 14
Concentration: International Business and others
Schools:Any offering one year MBA
WE 1: Information Tech
WE 2: Event Consultant for FIFA addi events and WC
Posts: 9
Kudos: 23
 [1]
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Nice compilation walker... When can we expect the complete material. :-)
User avatar
BarneyStinson
Joined: 21 Jul 2009
Last visit: 24 Sep 2010
Posts: 217
Own Kudos:
Given Kudos: 22
Concentration: World Domination, Finance, Political Corporatization, Marketing, Strategy
Schools:LBS, INSEAD, IMD, ISB - Anything with just 1 yr program.
Posts: 217
Kudos: 513
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Do it before this April bro!!!! Gotta brush my skills!!!!
User avatar
tarun
Joined: 30 Jun 2004
Last visit: 07 Mar 2011
Posts: 102
Own Kudos:
Given Kudos: 5
Location: Singapore
Posts: 102
Kudos: 102
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I missed circular arrangement while brushing up my concepts. Thanks for the good post.
User avatar
calvinhobbes
Joined: 21 Jan 2010
Last visit: 26 Mar 2013
Posts: 113
Own Kudos:
Given Kudos: 38
Kudos
Add Kudos
Bookmarks
Bookmark this Post
This is very helpful!
avatar
shahed052
Joined: 31 Jul 2009
Last visit: 27 Jul 2010
Posts: 1
Given Kudos: 1
Affiliations: Bangladesh National Cadet Corps(Army Wing),Dhaka University Film Society
Location: Bangladesh
Concentration: Ms in Finance
Schools:Texas A&amp;M,University of North Florida,University of Texas
GPA: 3.60
Posts: 1
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
many many thanks for the whole math collection...waiting for update and new one...
User avatar
TallJTinChina
Joined: 24 May 2010
Last visit: 28 Jun 2011
Posts: 38
Own Kudos:
Given Kudos: 4
Status:Waiting to hear from University of Texas at Austin
Location: Changchun, China
Concentration: MSA - Generalist
Schools:University of Texas at Austin, Michigan State
GPA: 3.9
Posts: 38
Kudos: 149
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Just read this post and the one about probability. A great help! Now I will try some application...
 1   2   
Moderator:
Math Expert
111171 posts