The sample mean and the sample standard deviation of annual returns on a stock over a 12- year period as computed by a stock analyst were 18% and 12%, respectively. The analyst wants to know if the risk, as measured by the standard deviation, differs from 15%. a. Construct a 90% confidence interval of the population variance and the population standard deviation. b. What assumption is required in constructing the confidence interval? c. Based on the above confidence interval, does the risk differ from 15%

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