Customers Arrive at a Single Self-Serve Coffee Machine in a Busy

Multiple Choice

Customers arrive at a single self-serve coffee machine in a busy mall at the rate of 20 per hour, following Poisson distribution. Each customer takes exactly 90 seconds to get his or her coffee. What is the expected number of customers in queue at this coffee machine?

A) 1.0
B) 1.5
C) 0.5
D) 2.0
E) 3.0