Question

A company produces electric devices operated by thermostatic control. The standard deviation of the temperature at which these controls actually operate should not exceed 2.0◦F. For a random sample of 20 of these controls, the sample standard deviation of operating temperatures was 2.36◦F.

i) Stating any assumptions you need to make, test, at the 5% level, the null hypothesis that the population standard deviation is 2.0 against the alternative that it is larger.

ii) Create a 90% confidence interval for the population variance.

Answer 1