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Point sequences reaching 4-4 under deuce rules

Question

In a game between two players, each point raises the winner's score by one, starting from 00-00. Reaching 44 points first wins the game, except that once the score has been 33-33 the winner must lead by two. How many different point-by-point sequences lead to the score 44-44?

Short answer

40=2(63)40=2\binom63. A 44-44 score is only possible if the game passed through 33-33 (otherwise someone would have reached 44 with a lead of two or more and won). There are (63)=20\binom63=20 orderings of the first six points, then the next two points must be split one each, in 22 orders.

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