Statistic
posted by Bibi .
Final averages are typically approximately normally distributed with a mean of 78 and a standard deviation of 11. Your professor says that the top 6% of the class will receive an A; the next 24%, a B; the next 41%, a C; the next 18%, a D; and the bottom 11%, an F. (Give your answers correct to one decimal place.)
(a) What average must you exceed to obtain an A?
(b) What average must you exceed to receive a grade of C or better?
(c) What average must you obtain to pass the course? (You'll need a D or better.)
You may need to use the appropriate table in Appendix B to answer this question.

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" (That should be Appendix B.) to find the proportions and their Z scores. Insert values in above equation and calculate for the scores.