Arrivals during the evening at a hospital emergency room are assumed to follow a Poisson distribution. The rate on Saturday evening is 2.5 per hour and on Sunday evening is 0.5 per hour.
(a) Find the probability of 6 or more arrivals on Saturday during the period 8pm to midnight.
(b) Find the probability of 2 or fewer arrivals on Sunday during the period 9pm to midnight, given that there is at least 1 arrival.