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GMAT Counting Methods http://www.800score.com/forum/viewtopic.php?f=3&t=2420 
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Author:  questioner [ Sun Jan 29, 2012 7:43 pm ] 
Post subject:  GMAT Counting Methods 
If each digit in the set A = {1, 2, 3, 4, 5} is used exactly once, in how many ways can the 5 digits be arranged? A. 6 B. 24 C. 72 D. 96 E. 120 (E) There are 5! = 120 possible arrangements of the five digits with no restrictions. Every time an item is selected, it is reduced from the pool. (5)(4)(3)(2)(1) = 120  Remember the rule of combination. 
Author:  Gennadiy [ Sun Jan 29, 2012 7:54 pm ] 
Post subject:  Re: t.1, qt. 17: combinatorics, permutations. 
Quote: Remember the rule of combination. In this question we deal with permutations.A combination would be some subset of a given set (order does NOT matter). For example, selecting three numbers out of five. 
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