A second red ball from the same urn
There are urns; urn () holds red ball and blue balls (so balls total). You pick an urn uniformly at random, draw a ball, and it is red. You replace it and draw again from the same urn. Let be the probability the second draw is also red. Compute .
Show hints (2)+
- Bayes: posterior on urn after a red draw . Then average over it.
- .
Answer
Reveal answer →Final answer
0.3333 (± 0.005)
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Asked at: Jane Street, Citadel