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.

11. Refer to Exhibit 1. If we are interested in determining an interval estimate for ? at 86.9% confidence, the
z value to use is

a. 1.96
b. 1.31
c. 1.51
d. 2.00

12. Refer to Exhibit 1. The value to use for the standard error of the mean is

a. 13.5
b. 9
c. 2.26
d. 1.5