question_answer 87)

Bag 1 contains 3 red and 4 black balls and bag II contains 4 red and 5 black balls. One ball is transferred from bag I to II and then a ball is drawn from bag II. He ball so drawn is found to be red in colour. Find the probability that the transferred bal is black. 

Answer:

Let E1 and E2 are the event that the ball transferred from bag I to II is black and it is red respectively.       Let R = event of drawing red ball from bag II. We get             P(the transferred ball is black) = P (E1/R)