A random sample of 25 4-wheel-drive pickups of the same year and model revealed the following miles per gallon (mpg) values:

12.4 13.0 12.6 12.1 13.1 13.0 12.0 13.1 11.4 12.6 9.5 13.25 12.4 10.7 11.7 10.0 14.0 10.9 9.9 10.2 11.0 11.9 9.9 12.0 11.3 Assume that the population for mpg for this model year is normally distributed.

a. Use the sample results to develop a 95% confidence interval estimate for the population mean miles per gallon.

b. Determine the average number of gallons of gasoline the pickups described here would use to travel between Los Angeles and San Francisco—a distance of approximately 400 miles.

c. Another sample of the same size is to be obtained.

If you know that the average miles per gallon in the second sample will be larger than the one obtained in part

a, determine the probability that the sample mean will be larger than the upper confidence limit of the confidence interval you calculated.