Engineering: Solar Batteries A set of solar batteries is used in a research satellite. The satellite can run on only one battery, but it runs best if more than one battery is used. The variance s 2 of lifetimes of these batteries affects the useful lifetime of the satellite before it goes dead. If the variance is too small, all the batteries will tend to die all at once. Why? If the variance is too large, the batteries are simply not dependable.

Why? Engineers have determined that a variance of s 2 5 23 months (squared) is most desirable for these batteries. A random sample of 22 batteries gave a sample variance of 14.3 months (squared).

(i) Using a 0.05 level of significance, test the claim that s 2 5 23 against the claim that s 2 is different from 23.

(ii) Find a 90% confidence interval for the population variance s 2.

(iii) Find a 90% confidence interval for the population standard deviation s .

AppendixLO1