Con 12 botes conteniendo cada uno 1/2 kg de pintura se han pintado 90 m de verja de 80 cm de altura. Calcular cuantos botes de 2 kg de pintura seran necesarios para pintar una verja similar de 120 cm de altura y 200 metros de longitud

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?