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391.The Witness Problem

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conditional probabilityCh. 2 — Axiomatic and Conditional Probability444+ Problems in Probability
Someone leaked IP from a quant firm! A witness claims the leaker was a trader. Witnesses are correct 2/32/3 of the time, and 2/32/3 of the firm's employees are traders (the rest are researchers). Given the witness's statement, what is the probability the leaker was a trader?

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