A bag contains 3 red balls, 5 yellow balls and 7 pink balls. If one ball is drawn at random from the bag, what is the probability that it is either pink or red?

Given number of balls = 3 + 5 + 7 = 15

One ball is drawn randomly = 15C1

probability that it is either pink or red =  $\frac{7C1 + 3C1}{15C1} = \frac{7 + 3}{15} = \frac{10}{15} = \frac{2}{3}$