How many courses do GSI’s usually teach?

GSI’s are usually assigned to one lecture course a semester and teach two smaller discussion sections of that course. GSI’s also have to attend the bigger lecture, offer office hours, and help in the grading of assignments and exams. Furthermore, they might have meetings with the members of the faculty teaching the larger course. However, the GSI appointments are 50%, thus the total number of hours per week that the GSI works is not more than 20.