A study of laws or mathematics did never count to be anything to achieve easily at University Cologne from 1980 to 1990. For Law: The median of achievement of students participating were the barrier to have passed. For Mathematics, achieve a level of 50% of weekly written exercise, otherwise you can't take the exam. Achieve 50% of the exam to pass it. If then the amount of students, who passed, were lower than 20% the level to pass might get corrected to only need 40% of the exam, even if than still only 30% will pass the exam.

I can recall one exam during my studies at University of Cologne with a similar situation. You needed to pass 50% of the weekly written exercise to participate in the exam. But less then 10 % achieved the final exam. The passing level got corrected so that the amount of people passing the exam were 40%.