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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.

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.

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.
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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
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"When the going gets tough, the tough gets going!"

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.

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

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.

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.
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“Keep your head down, and work hard. Don’t attract any attention. You should be grateful to be here.” Why do we keep quiet? Being an immigrant is a constant...

“Keep your head down, and work hard. Don’t attract any attention. You should be grateful to be here.” Why do we keep quiet? Being an immigrant is a constant...