The amount of time a bank teller spends with each customer has a population mean = 3.10 minutes and standard deviation = .40 minutes. If a random sample of 16 customers is selected without replacement from a population of 500 customers,
a. what is the probability that the average time spent per customer ill be at least 3 minutes?
b. There is an 85% chance that the sample mean will be below how many minutes?