CI = 95% alpha = 0.05 alpha/2 = 0.025
S^2 = 23.04 n = 29 Degrees of Freedom (DOF) = n-1 = 28
(n-1)S^2 (n-1)S^2
------------ < variance < ------------
chi-square 0.025 chi-square 0.975
28 DOF 28 DOF
chi-square 0.025 28 DOF = 44.46
chi-square 0.975 28 DOF= 15.30
28 * 23.04/44.46 < variance < 28 * 23.04/15.30
14.51 < variance < 42.16
3.8 < standard deviation < 6.49