Question

In Class XI of a school 40% of the students study Mathematics and 30% study Biology. 10% of the class study both Mathematics and Biology. If a student is selected at random from the class, find the probability that he will be studying Mathematics or Biology.

Answer 1

Let A be the event in which the selected student studies Mathematics and B be the event in which the selected student studies Biology.
Now,
P(A) = 40% = 40/100 = 2/5
P(B) = 30% = 30/100 = 3/10
P(A and B) = 10% =10/100 = 1/10
We know that P(A or B) = P(A) + P(B) – P(A and B)

Thus, the probability that the selected student will be studying Mathematics or Biology is 0.6.