A computer maker receives parts from three suppliers, S1, S2, and S3. Fifty percent come from S1, twenty percent from S2, and thirty percent from S3. Among all the
parts supplied by S1, 5% are defective. For S2 and S3, the portions of defective
parts are 3% and 6% respectively.
i. What portion of all the parts is defective?
ii. A customer complains that a certain part in her recently purchased computer
is defective. What is the probability that it was supplied by S2?