Asoftware company receives hundreds of support calls each day. there are several common installation problems, call them a, b, c and d. several of these problems result in the same symptom, lock up after initiation. suppose that the probability of a caller reporting the symptom lock up is .7 and the probability of a caller having problem a and a lock up is .6. given the caller reports a program lock up, what is the probability that the cause of the malfunction is problem a?