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Unformatted text preview: The rst basic principle is to multiply. Suppose we have 4 shirts of 4 dierent colors and 3 pants of dierent colors. How many possibilities are there? For each shirt there are 3 possibilities, so altogether there are 4 3 = 12 possibilities. An example, How many license plates of 3 letters followed by 3 numbers are possible? Answer: (26) 3 (10) 3 , because there are 26 possibilities for the rst place, 26 for the second, 26 for the third, 10 for the fourth, 10 for the fth, and 10 for the sixth. We multiply. How many ways can one arrange a,b,c ? One can have abc, acb, bac, bca, cab, cba. There are 3 possibilities for the rst position. Once we have chosen the rst position, there are 2 possibilities for the second position, and once we have chosen the rst two possibilities, there is only 1 choice left for the third. So there are 3 2 1 = 3! arrangements. In general, if there are n letters, there are n ! possibilities. 10...
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 Spring '10
 ansan
 Permutations And Combinations, Probability

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