bility that the sample tivum ive d. Explain the difference in the results of (a) and (c). SELF 7.8 According to the National Survey of Student En- TEST gagement, the average student spends about 17 hours each week preparing for classes; preparation for classes includes homework, reading and any other assignments. (Data extracted from "How much do you study.," usat.ly/1QrGlaj.) Assume the standard deviation of time spent preparing for classes is 4 hours. If you select a random sample of 16 students, a. What is the probability that the mean time spent preparing for classes is at least 16 hours per week? mad-EV eris noqu b. There is an 85% chance that the sample mean is less than how many hours per week? C. What assumption must you make in order to solve (a) and (b)? d. If you select a random sample of 64 students, there is an 85% chance that the sample mean is less than how many hours per week