1. Consider an experiment in which we record M(t), the number of active calls at a telephone switch at time t, at each second over an interval of 15 minutes. One trial of the experiment might yield the sample function m(t,s) shown in the figure below. Each time we perform the experiment, we would observe some other function m(t,s). The exact m(t,s) that we do observe will depend on many random variables including the number of calls at the start of the observation period, the arrival times of the new calls, and the duration of each call.

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