There are 100 students starting the Analytics program this semester and they have the option of taking 1, 2, or all 3 of these foundational courses: C1, C2, or C3. Adding up the enrollments in these three courses, we obtain 101. (a) Prove that at most one of the courses has an enrollment of 0. (b) Prove that exactly one student takes 2 courses.

Please help with part b). You can use part a) to help with the proof in part b). We need to use the principle of inclusion-exclusion.

Thanks