Question

A bag contains 3 red marbles and 4 blue marbles. then, 2 marbles are drawn from the bag, at random, "without replacement". if the first marble drawn is red, what is the probability that the second marble is blue

Answer 1

3 + 4 +2  = 9 total marbles

 If you pick a red one first and don't replace it that leaves a total of 8 marbles left

 there are 4 blue marbles

 so probability = 4/8, reduces to 1/2 probability of picking a blue marble