Most universities use a cost model to determine the tuition for students knowing that some students will be losses and some will be gains. Therefore, since it's a model, I can't directly answer your question but I can put it into a hypothetical. Let's say you have 30 students in a class and by adding one more student, you force that into two sections rather than one. Let's say the professor teaching the class already has reached their limit of sections and they are paid more to teach the additional section or another professor needs to be hired. If it's another professor, you are talking salary, retirement plans, pension, health insurance, sabbaticals, disability, tuition benefits, memberships to organizations, and a few others. Then you have to think about housing. If there are enough bed/rooms, not a big expense, except if you have to open a floor that wasn't currently being used. Then you have the added spend of the RA and extra water and supplies usage and maintenance. So adding one more student doesn't add more expense but adding 30 or, because you also need to add women's sports, 60 students, then the spends start to add up.