Many drivers of cars that can run on regular gas actually buy premium in the belief that they will get better gas mileage. To test this belief, we use 10 cars in a company fleet in which all the cars run on regular gas. Each car is
filled first with either regular or premium gasoline, decided by a coin toss, and the mileage for that tankful is
recorded. Then the mileage is recorded again for the same cars for a tankful of the other kind of gasoline. We
don't let the drivers know about this experiment. Here are the results in mpg. The first row is regular the bottom
row is premium