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Monday, February 8, 2016

Bang?


OK, we'll kickstart the week with a recent problem from the DataGenetics blog... a fairly simple, straightforward (...and morbid ;-) probability conundrum, I've re-written below:

I say "morbid" because it involves playing "Russian roulette" with the following twist... after duct-taping you to an IKEA chair a villain pulls out an empty 6-chamber gun and loads it (in your full view) with just two bullets in ADJACENT chambers. He closes the gun cylinder, gives it a good spin, points the barrel at your carefully-coiffed head, and pulls the trigger. CLIIIICK... no bullet... maybe you've lived to enjoy another day... or... NOT. 
The villain announces he is going to pull the trigger one more time, and if you're still alive you're then free to go merrily home, or to the nearest brew pub. He'll even give you a choice: he can pull the trigger again right where he left off, or he can re-spin the cylinder again first. Which should you have him do?
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answer:   pull the trigger without doing a re-spin... 75% chance of survival in that case (3 of 4 possible remaining chambers being blank)  vs. 2/3 chance of survival with a re-spin (4 out of 6 chambers empty) .  If that's not clear, follow link back to DataGenetics for fuller explanation; and they also worked out several further variations worth checking out.


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