In a finance class, the final grade is based on three tests. Historically, the instructor tells the class that the joint probability of scoring "A"'s on the first two tests is 0.5. A student assigns a probability of 0.9 that she will get an "A" on the first test. What is the probability that the student will score an "A" on the second test given that she scored an "A" on the first test?

0.50

0.95

0.55

0.90

The Probability of two As could be P(Two As(A))=.5 P(One A(B)) = .9 P(B/A)=?

I seem to be missing a variable here, like P(AuB).

I can multiply the two probabilities together and get .45 which should equal (AuB), but not sure of where to go from here.