Cliff has a bag of tennis balls. 8 are green, 7 are yellow and 5 are white. He picks a tennis ball at random. What is the probability that he picks one that is not green?

To solve this question, we need to know how many balls there are altogether in Cliff's bag. In total, there are 20 balls (8+7+5). We know that 8 of the balls are greens, so by subtraction (20-8) we can tell that the probability of picking a ball that is not green is 12/20. Usually, we try to simplify the fractions as much as possible before presenting it as an answer. In this case, we can divide both top and bottom numbers of the fraction by 4 to get the simplified answer 3/5!