CEO of a company that makes flashlight Datterles is trying to improve the product . In the past, this company's batteries would last an average of 8.5 hours with a standard deviation of 0.5 hours . There has been a change in the production method that the CEO claims will increase this time . A sample of 40 batteries made with this new procedure reveals that the mean running time is 8.7 hours with a standard deviation of 0.3 hours . a. The population mean () ) is The population standard deviation () is The sample size (n) is The sample mean (M ) is The sample standard deviation (s) is b. To calculate the z value for the one -sample z-test , we need all of the above values except for the c. What is the nondirectional null hypothesis in symbols ? (it has been started for you )