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A particular fast-food outlet is interested in the joint behavior of the random variable Y1, the total time between a customer's arrival at the store and his leaving the service window, and let Y2, the time that the customer waits in line before reaching the service. Since Y1 contains the time a customer waits in line, we must have Y1 242. The relative frequency distribution of observed values of Y1 and Y2 can be modelled by the probability density function = 9\" 053'2 53'1