A professor walks into a upper division statistics class and says, "I grade using a bell curve and z-scores. Whatever the range of grades happens to be, I will standardize the curve so that the mean will earn a C grade, and so will people in the range of +/- the class standard deviation. People in the range of one to two standard deviations above the mean will earn a B grade, and people who are above two standard deviations above the mean will earn an A grade. This will be true even if the mean of the class is 40% and the 90th percentile is 60%, which is possible because this class is very hard