This is outright stupid. You have my sympathies.
We don't curve at my school. If an exam question proves to be very difficult, then some questions are difficult. However, we do realize that if, say, if 80% of the the top quartile of the class get a question wrong, then it's not the Class, but either it's a bad question, or the faculty member taught the material poorly. these will be removed from the scoring.
Your instructors have every obligation to explain how classes are graded. Shame on them if they don't!