Question

You receive an A 40% of the time, a B 20% of the time, a C 15% of the time , and a D the rest of the time. For any random test, what is your expected grade point average? (Use the following values for X: A=4, B=3, C=2, D=1)

Answer 1

The grade you receive on a test is a discrete random variable with probability mass function

where the probability of getting a D is 25% because there are only 4 possible grades, and the probabilities must sum to 1 :

0.4 + 0.2 + 0.15 + 0.25 = 1

The expected test score/GPA is then

so your average would fall between a B and a C.