An urn contains a yellow balls and b purple balls. Balls are selected, one at a time, and discarded until a change in color occurs, at which time the last ball is returned to the urn. This process is repeated until the last ball is extracted. Let Pab denote the probability that the last ball in the urn is yellow. Show that Pa,b = 1/2. [Hint: Use induction on k= a +b and conditioning probability.] -