The best riddles. Anywhere.
Prisoner and Probability
posted by pinguhash - October 04 2011 01:27:31 AM
Once in prison there were 3 prisoners. One day the jailor informed all 3 that 2 of them will be set free and 1 will be hanged. The chance of each one's hanging is 1/3. One of the prisoner went to jailor and asked him whether he can tell him name of prisoner from other 2 who is going to set free. Jailor told he can't cos it will increase his chance of hanging from 1/3 to 1/2.
Prove that the jailor's thinking is wrong.
Reply by Ragib - October 05 2011 03:03:05 PM
jailor's naming one leaves other with half chance not to be,the unnamed person has .5*2/3 chance to,person asking name still has 2/3 probability to live and 1/3 to die.

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