Urn A: 2 white, 1 black, 3 red.
Urn B: 3 white, 2 black, 4 red.
Urn C: 4 white, 3 black, 2 red.
One urn is chosen randomly, 2 balls drawn, a red and a black.
Probability of choosing urn B: 1/3
Within urn B, probability of choosing red or black on ball 1: (2+4)/9 = 1/3
Within urn B, having chosen 1 red or black already, probability of choosing another red or black: 5/8
Probability urn B, then a red or black, then another red or black: 1/3 * 1/3 * 5/8 = 5/72 = 0.069444444 (4s forever).