Problem 5. (6 pts) Telephone calls arrive at an exchange at an average rate of one per second. Find the probabilities of the following events, explaining briefly your assumptions. (a) (2 pts) No call arrives during the first second. (b) (4 pts) Between 2 and 4 calls arriving in a given 5 second period. Hint: Use part (a), the bimonial distribution and the normal approximation