A school has 120 students. Each student attends 5 classes of different subjects and each class has 20 students and 1 teacher. If in a day, a teacher teaches 3 classes, what is the minimum number of teachers in the school?

The correct option is C 10
For 120 students, the number of classes needed $=\frac{120}{20}=6$

Each of 20 students attends 5 classes and these 5 classes of different subjects can be happening simultaneously.

So, number of classes needed to accommodate the students $=6\times 5=30$

Each teacher teaches 3 classes.
Hence, minimum number of teachers $=\frac{30}{3}=10$