Russian roulette

Interview question:

“Let’s play  russian roulette. You are tied to your chair and can’t get up. Here’s a gun. Here’s the barrel of the gun, six chambers, all empty. Now watch me as I put two bullets in the gun. See how I put them in two adjacent chambers? I close the barrel and spin it. I put the gun to your head and pull the trigger. Click! You’re still alive. Lucky you! Now, before we discuss your resume, I’m going to pull the trigger one more time. Which would you prefer, that I spin the barrel first, or that I just pull the trigger?” – How Would You Move Mount Fuji?

Answer (drag over the blank space below to see it):


If you choose to spin again the chances to be killed are 2/6 = 1/3 because any of the two bullets can be consumed after a spin.If you choose to pull the trigger directly then you know that the previously the used chamber was one of the four empty chambers. From the four empty chambers, only one is right before a bullet. Thus the probability to be killed in this case is is 1/4. So you would rather prefer not to spin again.


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