Question

a jar 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?

Answer 1

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;
$P(both\ red)=\frac{20\times19}{36\times35}=0.302$