3.41. A stock brokerage has four computers that are used for making trades on the New York Stock Exchange. The probability that a computer fails on any single day is 0.005. Failures occur independently. Any failed computers are repaired after the exchange closes, so each day can be considered an indepen- dent trial. (a) What is the probability that all four computers fail on one day? (b) What is the probability that at least one com puter fails on a day? (c) What is the mean number of days until a spe- cific computer fails?