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