The 50 could be interpreted as 50% or 50 out of an unknown point value. With the given information, the reader doesn't know how the subject did on the test. It can be assumed that the subject did not do equally well in each course since the 50 in psychology could be 50/50 and the 50 in chemistry could be 50/100. With more information, the reader might be able to come to a clearer answer