For each of the following sample results, construct the requested confidence interval. Assume the data come from normally distributed populations.
a. n = 12, xÌ„ = 28.4, s2 = 44.9;99% confidence for Ïƒ2
b. n = 7, xÌ„ = 28.4, s = 1.24;95% confidence for Ïƒ2
c. n = 20, xÌ„ = 28.4, s = 32;90% confidence for Ïƒ2
d. n = 17, xÌ„ = 28.4, s2 = 18.56;80% confidence for Ïƒ2