Question

During a test period, an experimental group of 10 vehicles using an 85 percent ethanol-gasoline mixture showed mean CO2 emissions of 240 pounds per 100 miles, with a standard deviation of 20 pounds. A control group of 14 vehicles using regular gasoline showed mean CO2 emissions of 252 pounds per 100 miles with a standard deviation of 15 pounds. A quick comparison of the sample variances suggests that the population variances are:

a. probably equal.
b. probably unequal.
c. incomparable.

Answer 1

Probably unequal ( B )

Explanation:

experimental group = 10

using 85% ethanol gasoline

mean = 240 pounds per 100 miles

standard deviation = 20 pounds

control group = 14 vehicles

using regular gasoline

mean = 252 pounds per 100 miles

standard deviation = 15 pounds

comparing the sample variance of each group shows that they are probably unequal using the equation below

Variance for a sample set of data = ∑ ( x - X ) ^2 / n - 1

where n = number of events

X = mean value

x = value of events