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Combinatorics Summary
[#permalink]
29 Jan 2012, 23:28
3
Kudos
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.
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Re: Combinatorics Summary
[#permalink]
30 Jan 2012, 02:32
1
Bookmarks
Expert Reply
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.
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.
Re: Combinatorics Summary
[#permalink]
30 Jan 2012, 02:41
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
Re: Combinatorics Summary
[#permalink]
30 Jan 2012, 02:58
Expert Reply
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.
Re: Combinatorics Summary
[#permalink]
30 Jan 2012, 03:38
2
Kudos
1
Bookmarks
Expert Reply
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
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.
Re: Combinatorics Summary
[#permalink]
18 Aug 2014, 01:04
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