Let x = the time between two successive arrivals at the drive-up window of a local bank. if x has an exponential distribution with λ = 1, (which is identical to a standard gamma distribution with α = 1), compute the following. (if necessary, round your answer to three decimal places.) (a) the expected time between two successive arrivals 1 (b) the standard deviation of the time between successive arrivals 1 (c) p(x ≤ 1) .632 (d) p(2 ≤ x ≤ 4) .117