Assume that the only grades possible in a history course are A, B, C, and lower than C. The probability that a randomly selected student will get an A in a certain history course is 0.18, the probability that a student will get a B in the course is 0.25, and the probability that a student will get a C in the course is 0.37.
a. What is the probability that a student will get an A OR a B?
b. What is the probability that a student will get an A OR a B OR a C?
c. What is the probability that a student will get a grade lower than a C?