A manufacturer of a gas additive claims that it improves gas mileage. A random sample of 30 drivers tests this claim by determining their gas mileage for a full tank of gas that contains the additive (X1) and for a full tank of gas that does not contain the additive (X2). The sample mean difference, D, equals 2.12 miles (in favor of the additive), and the estimated standard error equals 1.50 miles.
(a) Using t, test the null hypothesis at the .05 level of significance.
(b) Specify the p - value for this result.
(c) Are there any special precautions that should be taken with the present experimental design?