A normal population has a mean of 81 and a standard deviation of 6. You select a sample of 36. Use Appendix B.1 for the z values. Compute the probability that the sample mean is: (Round the z values to 2 decimal places and the final answers to 4 decimal places.) a. Less than 79. b. Between 79 and 83. c. Between 83 and 84. d. Greater than 84..