a bag contains 6 red,3 black and 6 white balls. a ball is selected at random from the bag.find the probablity that the selected ball is a)red or black
b)not black
a) probability of red or black = 6+3 / 15 = 9/15 = 3/ 5
b) prbability of black = 3/15 = 1/5
probability of not black = 1 - 1/5 = 4/5