Test analysis: suppose there are 20 students in this class, and each student is divided into 3 books, then the remaining 20 books; If everyone is divided into four books and there are still 25 books to read, then the equation can be solved.

There are three students in this class, which are deduced from the meaning of the question.

Solve?

There are three students in this class.

Comments: The key to solving this problem is to read the meaning of the problem, accurately find the relationship between quantity and quantity, correctly list the equations and then solve them.