If your class average is a 30-40%, there is either a problem with how the instructor teaches the materiel or how the instructor evaluates performance. In the first, no, the students have not learned the materiel well enough. In the second, it could go either way.
It is also possible that a test has 30% questions that C students will get, with the rest of the test being B and A student problems (with appropriate letter grade standards). If the class is mostly composed of C students, then they will get a 30-40% average.
@Spaceship wrote: “If your class average is a 30-40%, there is either a problem with how the instructor teaches the materiel or how the instructor evaluates performance. In the first, no, the students have not learned the materiel well enough. In the second, it could go either way.”
It’s also possible that everyone in the class was incredibly lazy or otherwise actually merited failing the class. Not necessarily terribly likely, but it’s a logical possibility, and so should be included in the list.