Statistics help

Question

A bag contains 5 black marbles, 9 white marbles, and 4 red marbles. If a marble is drawn from the bag, replaced, and another marble is drawn, what is the probability of drawing first a black marble and then a red marble?

Answer 1

18 total marbles, 5 black, 4 red.

event A = draw black marble on first draw

event B = draw red marble on second draw (w/o replacement)

P(A and B) = P(B|A)/P(A)

where P(B|A) is probability draw red marble given that black marble was drawn

P(A) = 5/18

P(B|A) = 4/17

P(A and B) = 4/17 * 5/18 = 10/153