A box is filled with 12 brown cards, 5yellow cards, and 3 green cards. A card is chosen at random from the box. What is the probability that it is a brown or a green card

probability (brown or green card) = total number of cards of brown and green / total number of cards of all color

so

total number of brown and green card = 12 + 3 = 15

total numbers of card = 12+5+3=20

probability (brown or green) = 15 / 20 = 3/4 = 0.75