A bank manager wishes to provide service for customers at the bank's drive-up window

Statistics Nov 10, 2020

A bank manager wishes to provide service for customers at the bank's drive-up window. The bank currently can serve up to 10 customers per 15-minute period without significant delay. The average arrival rate is 7 customers per 15-minute period. Let:
X = number of customers arriving per 15-minute period.
Find the probability that two or more customers arrive in a particular 15-minute period. (Round to three decimal places)