A federal regulatory agency is investigating an advertised claim that a certain device can increase the gasoline mileage of cars (mpg). Ten such devices are purchased and installed in cars belonging to the agency. Gasoline mileage for each of the cars is recorded both before and after installation. The data are recorded here.

Place 90% confidence intervals on the average mpg for both the before and the after phases of the study. Interpret these intervals. Does it appear that the device will significantly increase the average mileage of cars?

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installation. The data are recorded here. Car 12 3 4 5 67 89 10 Before (pg 19.1 29.9 176 20.2 23.5 26.8 21.7 25.7 19.5 28.2 10 2322 4.25 After (mpg) 25.8 237 28.7 25.4 32.8 192 29.6 22.3 25.7 20.1 10 25.33 425 Change (mpg 6.7 -62 111 5.2 9.3-76 7.9-34 6.2 -8.1 10 2.11 754