Problem 20: For a sample of nine automobiles, the mileage (in 1000s of miles) at which the original front brakepads were worn to 10% of their original thickness was measured,

as was the mileage at which the original rearbrake pads were worn to 10% of their original thickness. The results were given in the following table. Find and interpret a 95% confidence interval for the difference in mean lifetime between the front and rear brake pads.