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docabuzar
  Combinations [#permalink]
New postPosted: Tue Jan 24, 2012 2:18 pm 
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Two questions?

Q.1 What topics within combinotronics to cover for GMAT? Since there are so many variations in combinations, permutations, circular & linear arrangements.

Q.2 How to deduce the final result quickly if our formula shows something like this:
= 8! - (7!*2) - (5!*2) = ??


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Bunuel
  Re: Combinations [#permalink]
New postPosted: Tue Jan 24, 2012 2:41 pm 
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docabuzar wrote:
Two questions?

Q.1 What topics within combinotronics to cover for GMAT? Since there are so many variations in combinations, permutations, circular & linear arrangements.

Q.2 How to deduce the final result quickly if our formula shows something like this:
= 8! - (7!*2) - (5!*2) = ??


Hi, and welcome to GMAT Club!

Q #1: 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.

Q #2: 8! - (7!*2) - (5!*2) --> factor out 5!*2 --> 5!*2*(6*7*4-6*7-1)=240*125=30,000.

Hope it helps.

P.S. Please post general math questions in the main Math forum. Thanks.

_________________
RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?) - NEWEST SET OF TRICKY QUESTIONS!!!; 9 Bakers' Dozen (13 questions) - THIS WEEK'S ADDITION!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS - Latest set of tough DS questions; 9 Devil's Dozen!!! (13 questions) - THIS WEEK'S ADDITION!!!


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