Three urns A, B and C contain 7 red, 5 black; 5 red, 7 black and 6 red, 6 black balls, respectively. One of the urn is selected at random and a ball is drawn from it. If the ball drawn is black, then the probability that it is drawn from urn A is :
(3) 518
Bayes' theorem; each urn is chosen with probability 13:
P(A|black)= 13 512 13 512+ 13 712+ 13 612
= 55+7+6= 518
Answer: (3)
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