Question

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 A. If we are interested in determining an interval estimate for μ at 86.9% confidence, the z value to use is _____.

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

Answer 1

Answer:

so correct option is c. 1.51

Explanation:

given data

random sample n = 81

average speed x = 60 mph

standard deviation σ = 13.5 mph

interval estimate  μ =  86.9%

to find out

the value of the z

solution

we have given  μ =  86.9%

so we get here z critical value for the confidence level =  86.9 %

we will use here standard normal table

so z value for 86.9% is 1.51

so correct option is c. 1.51