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Unformatted text preview: 64 Permutations and CombinationsFACTORIALn! = n (n1) (n 2) 2 1e.g., 4! = 4 3 2 1Note: 4! = 4 3! In general, n! = n (n 1)!Permutation: a selection of a prespecified number of items from a given set of items, wheredifferent orderings of the same items are considered to bedifferent selections (and are counted separately)Example: set of items = {red, orange, yellow, green}some permutations, selecting 3 at a time:(red, orange, yellow)(orange, red, yellow)(yellow, green, red)(green, yellow, orange)are there any more? how many are there in all?you dont need to list them all and then count themHeres a formula (based on the multiplication principle):The number of permutationsof nthings taken rat a time is denoted by nPr, or Pn,rand the formula is:nPr= n (n  1) (n2)(for rfactors)(formula different from books but equivalent and easier to use)To answer the above question:The number of permutations of 4 things taken 3 at a time:4P3= 432 = 2464p. 1Combination...
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 Spring '11
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 Permutations, Permutations And Combinations

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