[net.puzzle] Ballot counting problem

tan@iwu1d.UUCP (William Tanenbaum) (02/29/84)

Here is a well known problem in probability which is difficult to
solve by brute force but yields easily to the proper insight:
---Two candidates run for office.  The winner receives p votes,
the loser receives q votes. (q<p obviously).  Suppose all the
ballots are mixed randomly before counting, and running totals
are kept as the votes are counted.  What is the probability that
the winner will always be ahead (never behind or tied) as the
votes are counted, (the inital 0-0 tie obviously excepted)?
Please prove that your answer is correct.  An answer without a proof
is no solution.  I will post the solution in a week if no one else
does first.
					Bill Tanenbaum
					A. T. & T. Bell Labs
					Naperville Il.