please juat answer letter D

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Students arrive at the Administrative Services Office at an average of one every 20 minutes, and their requests take, on average, 15 minutes to be processed. The service counter is staffed by only one clerk, Judy Gumshoes who works eight hours per day. Assume Poisson arrivals and exponential service times. a. What percentage of time is Judy idle? (Round your answer to 1 decimal place.) Percentage of time 250 % b. How much time, on average, does a student spend waiting in line?(Do not round intermediate calculations. Round your answer to 1 decimal place.) Average time 450 minutes c. How long is the (waiting) line on average? (Round your answer to 2 decimal places.) Average length of the waiting line 225 customers d. What is the probability that an arriving student (just before entering the Administrative Services Office) will find at least one other student waiting in line? (Do not round intermediate calculations, Round your answer to 2 decimal places.) Probably