Suppose that the amount of time that a battery functions is a normal random variable with a mean of 400 hours and a standard deviation of 50 hours. if two batteries are randomly picked with the intention of using one as a spare to replace the other if it fails, (a) what is the probability that the total life of both batteries will exceed 760 hours? (b) what is the probability that the second battery will outlive the first by at least 25 hours? (c) what is the probability that the longer-lasting battery will outlive the other by at least 25 hours?