A small local bakery offers a selection of 5 different types of cookies: chocolate chip, oatmeal raisin, peanut butter, snickerdoodle, and sugar cookies. Out of 50 customers surveyed, 20 preferred chocolate chip cookies, 10 preferred oatmeal raisin, 8 preferred peanut butter, 7 preferred snickerdoodle, and 5 preferred sugar cookies.

If a customer is chosen at random, what is the probability that the customer prefers either a chocolate chip cookie or a peanut butter cookie?