The grade you receive on a test is a discrete random variable with probability mass function
[tex]f_X(x)=P(X=x)=\begin{cases}0.4&\text{for }X=4\text{ (i.e. scoring an A)}\\0.2&\text{for }X=3\text{ (B)}\\0.15&\text{for }X=2\text{ (C)}\\0.25&\text{for }X=1\text{ (D)}\\0&\text{otherwise}\end{cases}[/tex]
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
[tex]\displaystyle\sum_x x\,f_X(x)=\sum_{x=1}^4 x\,P(X=x)=1\cdot0.25+2\cdot0.15+3\cdot0.2+4\cdot0.4=\boxed{2.75}[/tex]
so your average would fall between a B and a C.
