You draw two marbles from a bag containing 3 blue marbles,2 green marbles and 5 red marbles without replacement. what is the probability of drawing a red marble and then a green marble

The probability of drawing a red marble then a green marble would be 1/9.
In the first draw, there is a total of 10 marbles to choose from, and choosing a red marbles' probability would be 5/10, or 1/2. However in the second draw, there are only 9 marbles to choose from since you have already taken out a marble. Choosing a green marble in the second draw's probability would be 2/9. Using the rule P(A and B) = P(A) • P(B), we can also apply it to this problem "P(choosing a red marble first and then choosing a green marble second)" = 1/2 • 2/9, which is equal to 2/18. If you simplify that, you get 1/9.