# Re: Probability (orig. posted by rob77)(small correction)

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Posted by Joel on October 13, 2002 at 14:50:36:

In Reply to: Probability (orig. posted by rob77) posted by Joel on October 13, 2002 at 14:42:14:

There was a mistake in the lower right-hand corner of the chart on the original post which is corrected on this one (although it didn't affect the result).

: : A,B,C are evenly matched tennis players. Initially A and B play a set, and the winner then plays C. This continues, with the winner always playing the waiting player, until one of the players has won two sets in a row. That player is then declared the overall winner. What is the probability that A is the overall winner?

: I guess it IS a trick question, and the trick is that although all are evenly matched, A and B, by being in the first round, have an advantage over C.
: I don't know how to compute the probability but I believe it is a sum of the form 1/4 + 1/16 + 1/32 + 1/128 + 1/256 + 1/1024 + 1/2048 ... which seems to be approaching .375. (1/64 and 1/512 are intentionally omitted.
: Here is my "attempt" at an upside-down tree diagram of the possible outcomes, which (if the board displays it as I am hoping) may show how I am getting to that.

:
:

: AB

: AC BC

:
: **A** CB --BA-- CA 1/4

: --C-- BA -CB-- AB

: --B-- AC **A** BC 1/16

: **A** CB --B-- CA 1/32

: --C-- BA --C-- AB

: --B-- AC **A** BC 1/128

: **A** CB --B-- CA 1/256

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