During a test period, an experimental group of 10 vehicles using an 85 percent e

Question

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 = 0.05, in a left-tailed test, the critical value to compare the means (assuming equal variances) is:

A.1.321

-2.508

-2.074

-1.717

A.1.321

-2.508

-2.074

-1.717

Explanation / Answer

The correct option is D

Explanation:

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

for df=22, alpha=0.05 and left tail, by looking at a t table, we get
t=-1.717

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