Investors not only desire a high return on their money, but they would also like the rate of return to be stable from year to year. An investment manager invests with the goal of reducing volatility (year-to-year fluctuations in the rate of return). The following data represent the rate of return (in percent) for his mutual fund for the past 12 years.

(a) Verify that the data are normally distributed by constructing a normal probability plot.
(b) Determine the sample standard deviation.
(c) Construct a 95% confidence interval for the population standard deviation of the rate of return?

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