For each of the following sample results, construct the requested confidence interval. Assume the data come from normally distributed populations.

a. n = 12, ẍ = 28.4, s2 = 44.9; 99% confidence for σ2

b. n = 7, ẍ = 4.37, s = 1.24; 95% confidence for σ2

c. n = 20, ẍ = 105, s = 32; 90% confidence for σ2

d. n = 17, s2 = 18.56; 80% confidence for σ2\