The operations manager of a toll booth located at a major exit of a state turnpike is trying to estimate the average number of vehicles that arrive at the toll booth during a 1-minute period during the peak of rush-hour traffic. In an effort to estimate this average throughput value, he records the number of vehicles that arrive at the toll booth over a 1-minute interval commencing at the same time for each of 365 normal weekdays. The data are provided in the file P2_9.XLS. 

a. Choose a simple random sample of size 18 from the given frame to help the operations manager estimate the average throughput value. 

b. Compute a point estimate of the population mean from the sample selected in part a. What is the sampling error in this case? Assume that the population consists of the numbers of vehicle arrivals over the 365 weekdays in the given frame. 

c. Determine a good approximation to the standard error of the mean in this case. 

d. Repeat parts b and ¢ after generating a simple random sample of size 36 from the given frame.