Customers arrive at a grocery store at an average of 1.8 per minute. Assume that the number of arrivals ...

  

Customers arrive at a grocery store at an average of 1.8 per minute. Assume that the number of arrivals in a minute follows the Poisson distribution. Provide answers to the following to 3 decimal places.
 

Part a)
What is the probability that exactly two customers arrive in a minute? 

Part b)
Find the probability that more than three customers arrive in a two-minute period.