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Topic: Ace of Spades puzzle
Message: Posted by: Michael Daniels (Jun 14, 2021 06:12AM)
This posted today on the Guardian newspaper website.

https://www.theguardian.com/science/2021/jun/14/can-you-solve-it-ace-of-spades

Mike
Message: Posted by: cuchullain (Jun 14, 2021 09:51PM)
That first question is one of those infuriating puzzles that you do not want to believe the answers even when they were explained. I worked out 1 + 2 but still cannot believe 3!
A Keeper
Message: Posted by: Michael Daniels (Jun 15, 2021 02:30AM)
(3) seems so unbelievable because a "yes" answer is so improbable (1/52) that, in the vast majority of cases (51/52), the probability of guessing correctly is 1/51. It's hard to believe that the unlikely scenario when the card is actually the Ace of Spades can change matters so dramatically so that the overall probability is 1/26.

Intuitively it would seem even more implausible if a random number between 1 and 1000 was selected and you then asked "Is it 482?" But the theory remains the same and a Monte Carlo type simulation should confirm that the probability of guessing correctly in this case is 1/500.

Mike
Message: Posted by: cuchullain (Jun 15, 2021 05:00PM)
Chess engines can now use monte carlo simulation to coalesce around the best move