試題詳解

27. A hospital receives 1/5 of its flu vaccine shipments from Company X and the remainder of its shipments from other companies. Each shipment contains a very large number of vaccine vials.
For Company X’s shipments, 10% of the vials are ineffective. For every other company,2% of the vials are ineffective. The hospital tests 30 randomly selected vials from a shipment and finds that one vial is ineffective.
Calculate the probability that this shipment came from Company X.
(A) 0.10
(B) 0.14
(C) 0.37
(D) 0.63
(E) 0.86