Suppose the arrival of calls at a switchboard is modeled as a Poisson process with the rate of calls per minute being 
(a) What is the probability that the number of calls arriving in a 10-minute interval is less than 10?
(b) What is the probability that the number of calls arriving in a 10-minute interval is less than 10 if 
(c) Assuming 
what is the probability that one call arrives during the first 10-minute interval and two calls arrive during the second 10-minute interval?