Question

15. There are 40 students in a Chemistry class and 60 students in a Physics class. Find the number of students who are either in Physics class or Chemistry class in the following cases:
(i) The two classes meet at the same hour.
(ii) The two classes meet at different hours and 20 students are enrolled in both the subjects.

Answer 1

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Answer 2

Answer:

Let A be the set of students in chemistry class and B be the set of students in physics class. It is given that n(A)=40 and n(B)=60.

If two classes meet at different timings then there can be some student sitting in both the classes.

Therefore, n(A∩B)=20

n(A∪B)=n(A)+n(B)−n(A∩B)

=40+60−20=80.