There are 20 students in a chemistry class and 30 students in a physics class. find the number of students which are either in physics or in chemistry class in the following cases:
a)two classes meet at the same hour. (hint: n(C∩P) =Φ)
b)The two classes meet at different hours and 10 students are enrolled in both the courses. (hint: n(C∩P)=10)
We have given, n (C) = 20, n (P) = 30 and n (C ∪ P) = ?
(i) When two classes meet at the same hour i.e. no student can attained both the classes.
∴ n (C ∩ P) = 0
We know that,
n (C ∪ P) = n (C) + n (P) – n (C ∩ P) = 20 + 30 – 0 = 50
(ii) When two classes meet at different hours and it is given that n (C ∩ P) = 10
∴ n (C ∪ P) = n (C) + n (P) – n (C ∩ P) = 20 + 30 – 10 = 40