Ajar contains 36 marbles. it has 20 red, 12 black, and 4 green marbles. two marbles are drawn; the first is not returned before the second one is drawn. what is the probability that both marbles are red?

The probability of drawing red on the first draw is 20/36. Having drawn red on the first draw, the probability of drawing red on the second draw is 19/35. The probability that both marbles are red is therefore;