Of 200 surveyed students, 20% of those who read book A also read book B and 25% of those who read book B also read book A. If each student read at least one of the books, what is the difference between the number of student who read only book A and the number of who read only book B?
20% of those who read book A also read book B and 25% of those who read book B also read book A 这句话是什么意思啊……