Problem

1986 AIME Problem 13

In a sequence of coin tosses, one can keep a record of instances in which a tail is immediately followed by a head, a head is immediately followed by a head, and etc. We denote these by TH, HH, and etc. For example, in the sequence TTTHHTHTTTHHTTH of 15 coin tosses we observe that there are two HH, three HT, four TH, and five TT subsequences. How many different sequences of 15 coin tosses will contain exactly two HH, three HT, four TH, and five TT subsequences?

Leading zeroes must be inputted, so if your answer is 34, then input 034


Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.


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Problem Tags: Algebra Counting and probability

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