The combined gas mileage of midsize cars varies with mean 24 miles per gallon (mpg) and a standard deviation of about 5.5 mpg. A particular rental car agency typically has 150 midsize cars in its lot. Let  represent the mean combined gas mileage for all cars in the lot.
a) What's the approximate model for the distribution of ? Explain.
b) Estimate the probability that  is between 25 and 27 mpg.
c) There is only a 5% chance that the mean combined gas mileage is greater than what value?