Final averages are typically approximately normally distributed with a mean of 65 and a standard deviation of 8. Your professor says that the top 10% of the class will receive an A; the next 20%, a B; the next 41%, a C; the next 19%, a D; and the bottom 10%, an F. (Give your answers correct to one decimal place.)

Question

Final averages are typically approximately normally distributed with a mean of 65 and a standard deviation of 8. Your professor says that the top 10% of the class will receive an A; the next 20%, a B; the next 41%, a C; the next 19%, a D; and the bottom 10%, 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.)

Answer 1

You need to learn how to use a normal probability distribution curve, or tables. There is one at

http://psych.colorado.edu/~mcclella/java/normal/accurateNormal.html

I used it to get the following answers:
(a) A score = 75.3 or better
(b) C score or higher (top 71%) = 60.8
(c) Passing D score or higher (top 90%) = 54.7