Question: You wish to test the average life of the new Never-Ready batteries. According to Batteries Digest, the standard deviation of their lifespan is 8 hours.

a) Assuming a normal distribution, how many batteries would you have to test to be 99% confident of the average life with a tolerable error of 2 hours?

b) Given that the suggested sample size was used, how large would you expect the 99% confidence interval to be?