# Four balls in an urn. Probability.

An urn contains four balls, 2 white and 2 black. Balls are drawn one by one but just the three of them and we do not return them into the urn. What is the probability that: A={first drawn ball is black}, B={black ball is drawn at least once} and C={one white ball is drawn and two black}?

• Surely you must have some ideas, no? If you enumerate the balls as $W_1,W_2, B_1, B_2$ then you can just list all the possible triples. If you have no ideas at all, then this is one way to do it. – lulu Apr 13 '20 at 14:11