In constructing confidence intervals for s or s2, Table A-4 can be used to find the critical values x2Landx2L only for select values of n up to 101, so the number of degrees of freedom is 100 or smaller. For larger numbers of degrees of freedom, we can approximate x2Landx2Lby using

where k is the number of degrees of freedom and za/2 is the critical z score described in Section 7-2. Use this approximation to find the critical values x2Landx2rfor Exercise 9. How do the results compare to the actual critical values of 82.354 and 129.918?

[tea/2 + V2k - 1]2 2 2.