First, the denominator is the amount of subjects (for example colors). Say the question is find the probability of red. Say there is 4 blue dots, 9 red dots, 2 yellow dots, and 3 orange dots. The denominator would be 18 (the amount of dots). The numerator would be 9 because that is how many dots that were red are there. The answer would be 9/18 = 1/2. I hope his helps :)