Give the step-by-step reasoning process and then the final answer. A class has 60 students. The number of students who bring their lunch is thrice the number of those who eat in the school cafeteria. The rest of the students don't eat lunch. If 10 students eat in the school cafeteria, how many don't eat lunch?
Multiplying the number of students eating at the cafeteria by three means that 3 * 10 = 30 students bring lunch. The total number of students that eat lunch is 10 + 30 = 40 students. Since the class has 60 students, those who don't eat lunch are 60 - 40 = 20 students.
The final answer: 20.