Question: A local authority has a pool of cars available for staff to use on official business. One particular make and model of car, of which the authority has a considerable number, claims to give a miles per gallon (mpg) performance of 52 mpg for simulated out-of-town driving. For a sample of 20 cars the transport manager has calculated that the actual mpg for such driving has been 47 mpg, standard deviation of 7 mpg.
Based on this information would you conclude that the car manufacturer's claimed mpg is unrealistic? What assumptions have you had to make to reach a conclusion?