Prob.2 A computer maker receives parts from three suppliers S1, S2, and S3. Fifty percent come from S1, twenty percent come from S2, and thirty percent come from S3. Among all the parts that come from S1, 5% are defective. For S2 and S3, the proportion of defective parts is 3% and 6%, respectively. (a) What proportion of all the parts is defective? (b) A customer complains that a recently purchased computer has a defective part in it. What is the probability that it was supplied by S1?