Discussion:
Q: The McCollough Corporation, a producer of various kinds of batteries, has been producing D size batteries with a life expectancy of 87 hours. Due to an improved production process, the management believes that there has been an increase in the life expectancy of their D size batteries. A sample of 36 batteries showed an average life of 88.5 hours. Assume from past information that is known that the standard deviation of the population is 9 hours. Use a 0.01 level of significance and test management's belief.