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Students who are unable to understand a continuous function are not Harvard material anyway :-/
Harvard provides 100% of demonstrated need; just it works out that they cover all for those earning under $200k (plus all food/housing under $100k).
So e.g. if you make $210k/year in California with a family of 4, and the parents have $300k in cash and short term investments, they cover $45k -- or about 2/3rds of tuition. With $0 in investments, they cover $57k-- 90% of tuition.
If both kids are in college in this situation, they move to $65k, or slightly over 100% of tuition in this situation.
I do think the function could look pretty dang steep around $200k-- if you are in a low cost of living state with significant investments and one kid. But that's an edge case.