Two marbles are selected from a box containing 7 blue and 3 red marbles. what is the probability that a blue marble and a red marble are selected

Question

Two marbles are selected from a box containing 7 blue and 3 red marbles. what is the probability that a blue marble and a red marble are selected

Answer 1

Event A = P(select blue marble on 1st draw)

Event B = P(select red marble on 2nd draw)

P(A) = 7/10

P(B|A) = 3/9 = 1/3

P(A and B) = P(A) * P(B|A) = 7/10 * 1/3 = 7/30