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Topic: A nice math puzzle 


I came across this puzzle in a recent issue of The Actuarial Review (a newsletter for casualty actuaries). This newsletter has published quite a number of good math puzzles, and some math related magic tricks, over the years. This puzzle isn't a magic trick as such, but I think the method might be useful in an effect, somewhere, somehow. Here's a link to the puzzle: http://www.casact.org/newsletter/index.cfm?fa=viewart&id=3492 I don't want to spoil your fun right away, so I'll post the solution later ... although web savvy people should be able to find it on their own, without too much difficulty. 


Small question. Are any of the people allowed to change the position of the cards behind the curtains they looked at? N 


No. That would be a different puzzle, which might be worth exploring in its own right. But it's not allowed in this one. 


Great puzzle, balducci! At first thought, a solution didn't seem possible.... 


Right, okay, so I tried and tried and gave up and found the solution (you are correct, the web savvy should be able to find the answer in 10 seconds since it took me 20). That was painful, I had to work through it before I saw what was happening and I'm still a bit... irritated, lol. Carlos 


Try also looking here: http://www.rad.com/Article/0,6583,25604,00.html 


I managed to reach a probability of 5/12 which is 41.6666666% I assume it to be the maximum. or anybody has a better solution? 


The puzzle actually originates from a question in theoretical computer science. It was first stated by Peter Bro Miltersen and published in the paper "The Cell Probe Complexity of Succinct Data Structures" by Anna Gál and Peter Bro Miltersen. ([url]www.daimi.au.dk/~bromille/Papers/succinct.pdf[/url]). The solution to the puzzle was found by Sven Skyum. 