The preceding procedure

In Exercise 4.2.18 we found a confidence interval for the variance σ² using 

Exercise 4.2.18

Let  be a random sample from N(μ, σ2), where both param 

(a) Show that this second probability statement can be written as

(b) If n = 9 and s² = 7.93, find a 95% confidence interval for σ².

(c) If μ is known, how would you modify the preceding procedure for finding a confidence interval for σ²?