The Poisson probability formula is shown to the right, where X is the number of times the event occurs and is a parameter equal to the mean of X. This distribution is often used to model the frequency with which a specified event occurs during a particular period of time. Suppose that a hospital keeps records of emergency room traffic. These records reveal that the number of patients who arrive between 4 P.M. and 5 P.M. has a Poisson distribution with parameter = 3.6. Complete parts a through c. a. Determine the probability that, on a given day, the number of patients who arrive at the emergency room between 4 P.M. and 5 P.M. is exactly 5. P(X 5)=(Round to four decimal places as needed.) -22* P(X = x) = e x!