Question

The waiting times​ (in minutes) of a random sample of 22 people at a bank have a sample standard deviation of 4.2 minutes. Construct a confidence interval for the population variance sigma squaredσ2 and the population standard deviation sigmaσ. Use a 90% level of confidence. Assume the sample is from a normally distributed population.

Answer 1

Let's write the given information

n = sample size = 22

s = sample standard deviation = 4.2

Let's use minitab:

Step 1) Click on Stat>>>Basic Statistics >>1 variance...

Data : Select "sample standard deviation"

Sample size: 22

Sample standard deviation: 4.2

Step 2) Click on Option

Confidence level = 90

Alternative: Not equal

Then click on OK

Again Click on OK

So we get the following output:

From the above output the 90% Confidence Interval for population variance is = (11.3, 32.0)

And the 90% Confidence Interval for population standard deviation is = (3.37, 5.65)