Jacks and Aces
Logic puzzles require you to think. You will have to be logical in your reasoning.
A man has 3 cards face down on a table. One is a jack and two are aces. He knows the order but you do not. You can ask him one yes or no question, but when you do, you have to point to one of the cards. If you point to an ace, he will tell the truth, if you point to the jack, he will randomly say yes or no. You have to find one of the aces.
HintYes, there is always a chance you will be pointing to the jack, and that the answer will be meaningless (just a random yes/no) but there is a way to work around it. Don't give up!
Point to the middle card and say, "Is the card to the right an ace?" If the answer is yes, then the card on the right is an ace. If the answer is no, the card on the left is an ace. This solution works because if you're pointing to an ace then he's obviously telling the truth and if you're pointing to the jack the answer doesn't matter anyway because you will pick one of the other two which are both aces.
Sep 26, 2001
|Ok, you didn't say they were in a line.|
Dec 03, 2001
|Plus, I'd just pick one. I have a 66.67% chance of picking an ace, and thouse are pretty good odds.|
May 29, 2002
|SO Jack you would prefer 66.7% to 100% chance?|
Oct 11, 2003
|This is a really good one. I tried hard but couldn't get it.|
Feb 08, 2006
Mar 12, 2006
|I was convinced there was no solution until I read the answer. Good one!|
Apr 08, 2006
|that can't be right. that would mean there is always an ace to the right... what if the jack was there|
Jun 22, 2006
|if the jack was on the right, you must have been pointing to an Ace, which means he would tell the truth, and tell you that there is no Ace to the right of the card you are pointing to....choose the left card, it has to be an ace.|
Aug 04, 2008
|Kudos for originality, and double for stumping me!|
My lame solution was to point at a card and ask, "Is my mother's mother's maiden name 'Thomas'?" If were pointing at a an ace, the man would balk, not knowing the answer, but a Jack would get me a 'yes' or 'no'.
Your solution is, of course, more proper and elegant.
Dec 14, 2012
|Another question could be to ask "Does your middle card borders an Ace?" If the answer is yes, we know it is true and the middle card is an Ace. If the answer is no, the middle card is a Jack and other cards are Aces.|
Jan 22, 2017
|frazen: your theory is flawed because if its a jack the guy can say both yes and no. so if you ask the bordering question and middle is jack he can say both yes and no.|
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