I don't have exact answers to your questions, but it basically comes down to the endowment. For example Princeton has an endowment of 29 billion dollars. There

I don't have exact answers to your questions, but it basically comes down to the endowment. For example Princeton has an endowment of 29 billion dollars. There are 8,623 undergrads, and if you assume the full sticker price for tuition, room, board, and expenses ($75,210) reflects the actual cost, then it costs $648,535,830 per year to educate those students. That's 2.5% of the endowment if you assume nobody is paying anything and that it reflects the true cost; but the endowment grows by more than that annually just from investment returns!