Write an expression to describe the sequence below. use n to represent the position of a term in the sequence, where n = 1 for the first term. -7, -14, -21, -28, …

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?