Two major automobile manufacturers have produced compact cars with engines of the same size. We are interested in determining whether or not there is a significant difference in the mean MPG (miles per gallon) when testing for the fuel efficiency of these two brands of automobiles. A random sample of eight cars from each manufacturer is selected, and eight drivers are selected to drive each automobile for a specified distance. The following data (in miles per gallon) show the results of the test. Assume the population of differences is normally distributed.
Driver Manufacturer A Manufacturer B
1 32 28
2 27 22
3 26 27
4 26 22
5 25 24
6 29 25
7 31 26
8 25 27
The mean of the differences is
a. .5.
b. 2.0.
c. 1.5.
d. 2.5.