You have a box containing 6 white, 4 red, and 8 black marbles. You pick a marble and it is red. You then pick a white marble. On the third attempt, you pick a white marble again. What are the chances that on the fourth try you will pick a black marble? (Hint: You have not replaced the marbles you picked).
If you initially have 6 W, 4 R, and 8 B, and you take away two whites and a red, then you have 4W, 3 R and 8 B. There are 15 marbles total, and 8 black marbles, so you have an 8 in 15 or 53% chance of picking a black marble.
