Customers arrive at a computer store according to a Poisson process with 5 customers expected per hour. The sales force can accommodate at most 10 customers per hour; if more than 10 customers appear in an hour, the excess must be turned away.

(a) What is the probability that customers are turned away in a 1-hour period?

(b) Consider two independent 1-hour intervals. Let X denote the number of arrivals during the first hour and Y the number of arrivals during the second hour. Find P(X + Y ≤ 8).