Start with an urn with 5 red and 3 blue balls in it. Draw one ball. Put that ball back in the urn along with another ball of the same color. Now draw another ball from the urn.Suppose the second ball is red. What is the probability the first ball was blue.
The answer is 1/3, but why can't I use Bayes Theorem for this?
P(D1 = B | D2 = R) = P(D2 = R | D1 = B) * P(D1 = B) / P(D2 = R) = 5/10 * 3/8 / (5/8) = 3/10