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Picking cards (Posted on 2006-08-17) Difficulty: 3 of 5
A player picks random cards from an ordinary card deck, without returning them to the deck. How many cards should he pick so as to get at least one ace with 70% probability?

No Solution Yet Submitted by atheron    
Rating: 3.0000 (1 votes)

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re(2): solution -- spoiler | Comment 3 of 7 |
(In reply to re: solution -- spoiler by Penny)

Indeed, even theoretically, 13 draws will bring the closest to a 70% probability of at least one ace: a 69.62% probability. With 14 draws he has a 72.73% probability.  I guess I was reading the question as "at least one ace with at least 70% probability." One could also interpret it as "at least one ace with as close to 70% probability as possible," in which case 13 would fit the bill.
  Posted by Charlie on 2006-08-17 20:08:42

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