Question 99847
Since the probability of a red ball is 2/3 after a blue one was picked 2/3 of the balls in the bag are red.
2/3,4/6,6/9,8/15
before the 1st ball was drawn the probability of drawing a red was
2/4,4/7,6/10,8/16
8/16*8/15=64//240=4/15 eureka!
so the probability that the 1st ball is blue = 8/16 or 1/2
Ed