2 black marbles:
1 white, 1 black:
1 white, 1 non-black (this means you draw either 2 white, or 1 white and 1 red; we add the events' probabilities because they are disjoint events):
1 white, 1 black:
1 white, 1 non-black (this means you draw either 2 white, or 1 white and 1 red; we add the events' probabilities because they are disjoint events):