How about getting an average score of 60 in math class and 75 in the exam?
Normal. The full score of the first grade math class is 150, with an average score of 60. It's normal to get 70 points in the exam. Most students are poor at math, and many students can only get 20 or 30 points in the exam, so the average score in a class is 60 points, which is normal, but it is already very good.