Question

A box contains 4 white and 5 black balls. A ball is drawn at random and its colour is noted. A ball is then put back in the box along with two additional balls of its opposite colour. If a ball is drawn again from the box, then the probability that the ball drawn now is black, is A. 7 11 B. 5 11 C. 53 99 D. 48 99 Select the correct answer from above options

Answer 1

Correct Answer - C Consider the following events : E1 =Ball drawn from the box is white E2 =Ball drawn from the box is black A= Getting a black ball from the box after replacing the drawn ball with two balls of opposite colour P(E1)= 4 9 ,P(E2)= 5 9 ,P(A/E1)= 7 11 ,P(A/E2)= 5 11 ∴P(A)=P(E1)P(A/E1)+P(E2)P(A/E2) = 4 9 × 7 11 + 5 9 × 5 11 = 53 99