population variance (Google’s “true” variance) is 0.02%. The chi-square variable = 38.14:

Sample variance (30 days) 0.0263%

Degrees of freedom (d.f.) 29

Population variance? 0.0200%

Chi-square variable 38.14 = 0.0263%/0.02%*29

**=CHIDIST() = p value 11.93% @ 29 d.f., Pr[.1] = 39.0875**

Area under curve (1- ) 88.07%

How did we arrive at the value of 11.93? What formula do we use for approximation?