A manufacturer of calculators buys integrated circuits from supplies A,B and C. Fifty percents of the circuits come from A, 30% from B and 20% from C. One percent of the circuits supplied by A have been defective, 3% of Bs have been defective and 4% of C has been defective in the past.

(a) Suppose that a circuit is randomly selected. What is the probability that it is defective
(b) A circuit is selected at random and found to be defective. What is the probability it was manufactured by A?