The manager of the service department of a local car dealership has noted that the service times of a sample of 15 new automobiles has a standard deviation of 4 minutes. A 95% confidence interval estimate for the variance of service times for all their new automobiles is
A)8.576 to 39.796
B)4 to 16
C)4 to 15
D)2.93 to 6.31

Question

Quizplus · Accepted Answer

The confidence interval for the variance is calculated using the chi-square distribution. With a sample size of 15, the degrees of freedom is 14. Using the chi-square values for 95% confidence, the interval for the variance is calculated as 8.576 to 39.796.

The Manager of the Service Department of a Local Car