MATH 151 Lecture 4: September 21st - 1.5 Combinations
22 Mar 2016
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=6720: how many arrangements have the three a"s consecuive, glue all the a"s together to get one leter (aaa, arrange the new set of leters: aaa, c, d, e, m, i. = 720: how many arrangements have all 5 vowels adjacent, in any order, glue vowels together: =20: then arrange the 4 new leters: vowels, c, d, m, muliply the answers of each step together 20 x 24 = 480. Combinaions: an unordered selecion of objects r n = c (n,r) = ncr ncr = npr / r! Denotes the number of combinaions of r objects selected from n disinguishable objects. Alex inds 9 books that he wants to buy, but he can only aford 3. Pat has inherited 45 artworks and wants to donate 7 pieces to each of her 4 favourite aucions. How many ways can she do this? (45 c 7)(38 c 7)(31 c 7)(24 c 7)
