The manager of the service department of a local car dealership has noted that the service times of a sample of 30 new automobiles has a standard deviation of 6 minutes. A 95% confidence interval estimate for the standard deviation of the service times for all its new automobiles is _____.
A) 16.05 to 45.72
B) 4.78 to 8.07
C) 2.93 to 6.31
D) 22.83 to 65.06

Question

Quizplus · Accepted Answer

To estimate the confidence interval for the standard deviation of a population based on a sample, we use the Chi-Square distribution. The formula involves the sample standard deviation, the sample size, and the Chi-Square values for the desired confidence level. The correct interval is calculated using the Chi-Square distribution values for 29 degrees of freedom (n-1) at the 95% confidence level, which results in the interval 4.78 to 8.07.

The Manager of the Service Department of a Local Car