# A wrong reasoning about conditional probability

Two of three prisoner A, B and C will be executed, A asks the name of one other than A himself who will be executed. Jailer says that it is B. Merely by asking the question, A reduced the probability that he will be executed from 2/3 to 1/2, regardless of which answer.

What is wrong with the reasoning? I think the key is jailer answer the question by excluding the situation of A. So the answer just reduced the probability that C will die. A had better ask a question like if B will be executed but I want to ask the accurate reasoning by some formula.

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Ops, nevermind. – M.B. Jun 15 '12 at 12:43
"merely by asking the question,A reduced the probability that he will be executed from 2/3 to 1/2,regardless of which answer.what is wrong with the reasoning?" What is wrong with which reasoning? There is no reasoning in your question up to that point, just a bald (and wrong) assertion that the probability suddenly changes. – Henning Makholm Jun 15 '12 at 12:59