The makers of the MAGNETIZER Engine Energizer System (EES) claim that it improves gas mileage and reduces emissions in automobiles by using magnetic free energy to increase the amount of oxygen in the fuel for greater combustion efficiency. Following are test results, performed under international and U.S. Government agency standards, on a random sample of 14 vehicles. The data give the carbon monoxide (CO) levels, in parts per million, of each vehicle tested, both before installation of EES and after installation.

Suppose that you want to perform a hypothesis test to determine whether, on average, EES reduces CO emissions. Conduct preliminary graphical data analyses to decide whether applying the paired t-test is reasonable. Explain your decision.

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Before After Before After 1.60 0.15 260 1.60 0.30 0.20 0.15 0.06 3.80 280 0.06 0.16 6.20 3.60 0.60 0.35 3.60 1.000.03 0.01 50 050 0.10 0.00 2.00 160.00