During a test period,an experimental group of 10 vehicles using an 85 percent ethanol-gasoline mixture showed mean CO2 emissions of 667 pounds per 1000 miles,with a standard deviation of 20 pounds.A control group of 14 vehicles using regular gasoline showed mean CO2 emissions of 679 pounds per 1000 miles with a standard deviation of 15 pounds.At α = .05,in a left-tailed test,the critical value to compare the means (assuming equal variances)is
A)−2.508
B)−2.074
C)−1.321
D)−1.717

Question

Quizplus · Accepted Answer

To find the critical value for a left-tailed test with α = .05 and assuming equal variances, we need to use the t-distribution with degrees of freedom given by:

df = (n1 + n2 - 2) = (10 + 14 - 2) = 22

Using a t-table or a calculator, we can find that the critical value for t with 22 degrees of freedom and α = .05 for a left-tailed test is approximately -1.717. Therefore, the answer is D.

During a Test Period,an Experimental Group of 10 Vehicles Using