Maria makes a revolving shelf out of wood. The top of the revolving shelf is a circular piece of wood with a diameter of 20 inches. What the area of the top of the revolving shelf, in square inches?

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?