standard error and probability

Power+. produces AA batteries used in remote-controlled toy cars. The mean life of these batteries follows the normal probability distribution with a mean of 20 hours and a standard deviation of 5 hours. As a part of its testing program, Power+ tests samples of 25 batteries. Use Appendix B.1 for the z-values. a. What can you say about the shape of the distribution of sample mean? Shape of the distribution is (Click to select) v b. What is the standard error of the distribution of the sample mean? (Round the final answer to 4 decimal places.) Standard error c. What proportion of the samples will have a mean useful life of more than 21 hours? (Round the final answer to 4 decimal places.) Probability d. What proportion of the sample will have a mean useful life greater than 19.5 hours? (Round the final answer to 4 decimal places.) Probability e. What proportion of the sample will have a mean useful life between 19.5 and 21 hours? (Round the final answer to 4 decimal places.) Probability