Saturday, February 9th, 2013
Question : There are 4 red & 5 green balls in bag A and 5 red & 6 green balls in bag B. If a bag is selected at random and a ball is selected from that, what is the probability that it is red?
Probability of Red Ball = Bag A is selected & Red Ball is selected + Bag B is selected & Red Ball is selected
(1/2)*(4/9) + (1/2)*(5/11) = (1/2)[ (44+45) / 99 ] = 89/198