There are 40 students in a chemistry class and 60 students in a physics class.What is the number of students either in physics or chemistry class in the following cases: (i) the two classes meet at the same hour. (ii) the two classes meet at different hour and 20 students are enrolled in both the subjects.

Whwn two classes meet at the same hour means separate 40 and 60 students are there in both classes
That means total of 100 student

When two classes meet at different hours means some students can be common which in this case is 20. So total students will be 60 + 40 – 20 i.e. 80 ( Since these 20 students were counted twice)