Wait time for passengers at a ferry is normally distributed with = 8 minutes and = 2 minutes. Suppose you select a random sample of 25 passengers.

a) What is the probability that the sample mean is less than 9 minutes?

b) If now, you select a random sample of 36 passengers, what is the probability that the sample mean is less than 9 minutes?

c) Explain the difference between your answers to parts a) and b).