#14

Find the critical value t_c for the confidence level c=0.90 and sample size n=27.

t_{c =} ________ (round to the nearest thousandth as needed)

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# 30

The waiting times (in minutes) of a random sample of 20 people at a bank have a sample standard deviation of 4.2 minutes. Construct a confidence interval for the population variance 2 and the population standard deviation . Use a 99% level of confidence. Assume the sample is from a normally distributed population.

What is the confidence interval for the population variance 2?_______,________ (round to two decimal places as needed).