Sixteen cars are ?rst driven with a standard fuel and then with Petrocoal, a gasolin with a methanol additive. The results of the nitrous oxide emissions (NOx) test are as follows:
Type of fuel Average NOx Standard deviation of NOx
Standard 1:075 0:5796
Petrocoal 1:159 0:6134
Source: Micheal O. Finkelstein and Bruce Levin, Statistics for Lawyers,
Spring-Verlag, New York, 1990, p.230.
a. How would you test the hypothesis that the two population means are the same?