Suppose you buy a new car whose advertised mileage is 25 miles per gallon (mpg). After driving your car for several months, you find that its mileage is 21.4 mpg. You telephone the manufacturer and learn that the standard deviation of gas mileages for all cars of the model you bought is 1.15 mpg.
a. Find the z-score for the gas mileage of your car, assuming the advertised claim is correct.
b. Does it appear that your car is getting unusually low gas mileage? Explain your answer.