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Counting Permutations When Indistinguishable Objects May Exist

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Presentation on theme: "Counting Permutations When Indistinguishable Objects May Exist"— Presentation transcript:

1 Counting Permutations When Indistinguishable Objects May Exist
How many rows , each one consisting of 3 A’s 1 B, and 4 C’s are there? (Here are some such rows: BACCCAAC ABCACACC CCCCAAAB Etc.) Answer: (3+1+4)! / (3!1!4!).

2 In general: k distinct types of objects are given, where k is a positive integer. Positive integers ni for i=1,…k are given. k is a given positive integer. How many rows are there, each one including ni objects of type i for i=1, …, k and no other objects? Answer: Let n=n1 + … +nk. Then the number of rows is n!/(n1! … nk!).


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