For a sample of size 11, the critical values of chi-square for a 90 percent confidence interval for the population variance are: A)6.262, 27.49 B)6.908, 28.85 C)3.940, 18.31 D)3.247, 20.48 d.f. = n - 1 = 10, we get χ²_L = 3.940 and χ²_U = 18.31 from AppendixE.

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We use the formula for degrees of freedom, df = n - 1 = 11 - 1 = 10. From Appendix E, with a 90% confidence interval, the chi-square values are χ²_L = 3.940 and χ²_U = 18.31. Therefore, the best choice is C, which contains these values.

For a Sample of Size 11, the Critical Values of Chi-Square