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The length of time of calls made to a support helpline follows an exponential distribution with an average duration of 20 minutes so thatA = % = 0.05. (Round your answer to four decimal places.) (a) What is the probability that a call to the helpline lasts less than 10 minutes? (b) What is the probability that a call to the helpline lasts more than 35 minutes? (c) What is the probability that a call lasts between 20 and 30 minutes? (d) Tchebysheff's Theorem says that the interval 20 :t 2(20) should contain at least 75% of the population. What is the actual probability that the call times lie in this interval