Three boxes contain red balls only. Box A has 2, Box B has 5 and Box C has 3 balls. If a box is chosen at random and then a ball selected, probability it came from Box B given that a red ball was obtained is:

Three boxes contain red balls only. Box A has 2, Box B has 5 and Box C has 3 balls. If a box is chosen at random and then a ball selected, probability it came from Box B given that a red ball was obtained is:

• A. 1/3
• B. 1/2
• C. 5/10
• D. 3/10

Answer: A) 1/3

Explanation: Every draw gives red. Hence information adds nothing. Probability chosen Box B=1/3.