Volume 9: Friend, Have you Bought Insurance?

In the fifth class in the second grade of Zhi Xin High School, the mathematics teacher was explaining the multiplication of fractions with a common denominator at the front of the class. Some of the students were sleeping, some secretly ate some potato chips from their drawers, some used their textbooks to block the teacher from seeing that they were playing Kings of Glory on their phones, and some were just chatting and laughing in a whisper. 

The teacher was already accustomed to this. After explaining an example, he knocked on the blackboard and asked the students to write it down. Among the large number of students who did whatever they wanted, only one person was taking down notes. The teacher was very grateful to have even one student like this.

He planned to ask...