The mean of 5 numbers is 8. one more number is added to the group.
the mean of the numbers is 9.
what number was added to the group​

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?