Mark has one blue dress shirt, one white dress shirt, one black dress shirt, one pair of black slacks, one pair of grey slacks, and one red tie. all six of his possible outfits are listed below. let a aa be the event that mark's little brother selects an outfit with a white shirt and grey slacks and b bb be the event that he selects an outfit with a black shirt. what is p ( a or b ) p(a or b)p, left parenthesis, a, start text, space, o, r, space, end text, b, right parenthesis, the probability that mark's little brother selects an outfit with a white shirt and grey slacks or an outfit with a black shirt?