Starting with 10 blue balls, in each of 10 sequential rounds, we remove a random ball and replace it with a new red ball. for example, after the first round we have 9 blue balls and one red ball, after the second round, with probability 9/10 we have 8 blue balls and 2 red balls, and with probability 1/10 we have 9 blue balls and one red ball, etc. what is the probability that the ball we remove at the 11th round is blue?