In a class, there are 80 students who study both Computer Science and Electronics. While 100 students study Computer Science, 120 students study Electronics. How many of them study Computer Science only?

According to above given question , we can say that
There are 100 students in Computer Science which include students of electronics too.
Numbers of students who study both Computer Science and Electronics = 80
∴ Number of students opting for Computer Science only = 100 – 80 = 20
Therefore , 20 students study Computer Science only .