Hel 2. Patients arrive at a hospital accident and emergency department at random follow a
Poisson distribution at a rate of 6 per hour.
(a) Find the probability that, during any 90-minute period, the number of patients
arriving at the hospital accident and emergency department is
(i) exactly 7
(2 marks)
(ii) at least 3
(2 marks)
(b) What is the mean and standard deviation of the number of patients arriving at the
hospital accident and emergency department in an hour?
(2 marks)