The number of customers arriving at the checkout counter in a department store during a one hour period is a Poisson random variable with parameter ? = 7. What is the probability of:
(a) 5 customers a rriving between 10:00 - 11:00?
(b) 10 customers arriving between 10:00 - 12:00?
(c) 3 customers arriving between 10:00 - 10:30?