Urn I contains 4 White, 5 Black balls. Urn II has 3 White, 4 Black. One ball is transferred from Urn I to Urn II, then a ball drawn from Urn II is found to be White. The probability the transferred ball was White is:

Urn I contains 4 White, 5 Black balls. Urn II has 3 White, 4 Black. One ball is transferred from Urn I to Urn II, then a ball drawn from Urn II is found to be White. The probability the transferred ball was White is:

• A. 15/31
• B. 16/31
• C. 4/9
• D. 1/2

Answer: B) 16/31

Explanation: P(W trans|W drawn) = [P(W drawn|W trans)P(W trans)] / Total P(W drawn) = [(4/8)×(4/9)] / [(4/8×4/9) + (3/8×5/9)] = 16 / (16 + 15) = 16/31.