Bag A holds 2 red and 3 blue balls; bag B holds 4 red and 1 blue. A bag is chosen at random and one ball drawn. It is red. What is the probability it came from bag A?
Answer and explanation
Correct answer: D.
- Step 1: and . Step 2. Bayes: . **Answer: . Why not the others:** 2/5 ignores bag B; 1/2 ignores the evidence; 3/5 is the probability of red, not of bag A.
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