ok..here's a nice Q........there are n urns.....each urn contains 'a' white and 'b' black balls........i first pick up one ball at random from the first urn and place it inside the second urn.....then pick up a ball at random frm the second urn and put it into the 3rd urn........and pick up a ball at random frm the 3nd urn and put it into the 4th urn and so on.......after the whole process is over....wats the probability that a randomly picked up ball from the 'k'th urn turns out to be a white ball.........