posted by Emma .
Suppose cars arrive at Burger King's drive-through at the rate of 20 cars every hour between 12:00 noon and 1:00 pm. A random sample of 40 one-hour periods between 12:00 noon and 1:00 pm is selected and has 22.1 as the sample mean number of cars arriving. (a) Why is the sampling distribution of the sample mean approximately normal? (b) Assuming and , what is the mean and standard deviation of the sampling distribution? What is the probability that a simple random sample of size n = 40 one-hour time periods results in a mean of at least 22.1 cars?