Saved Help S 9 The mean of a normal probability distribution is 280; the standard deviation is 30. Refer to the table in Appendix B1. (Round the fine answers to 2 decimal places.) a. About what percentage of the observations lie between 250 and 310? Percentage of observations % 01:42:29 b. About what percentage of the observations lie between 220 and 340? Percentage of observations % c. About what percentage of the observations lie between 190 and 370? Percentage of observations %