Exhibit 8-3 A Random Sample of 81 Automobiles Traveling on a Section

Multiple Choice

Exhibit 8-3
A random sample of 81 automobiles traveling on a section of an interstate showed an average speed of 60 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph.
-Refer to Exhibit 8-3. The value to use for the standard error of the mean is

A) 13.5
B) 9
C) 2.26
D) 1.5