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BS: Logic puszzle
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BS: Logic puszzle |
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Subject: BS: Logic puszzle From: GUEST,MMario Date: 07 Jul 05 - 03:06 PM Just got this from a friend. trying to verify my answer. One day two students, Mr. P and Mr. Q are doing a test with Prof John. They know there are 16 cards in the drawer, Heart: A Q 4 Spade: J 8 4 2 7 3 Club: K Q 5 4 6 Diamond: A 5 Prof John drew one card from the group. He told Mr. P the face value of the card and told Mr. Q the suite of the card. Here is the conversation between them, Prof John: Do you know which card it is? Mr. P: I cannot tell which card it is. Mr. Q: I know you cannot tell. Mr. P: Based on what you just said, I know which card it is now. Mr. Q: Well, I also know which card it is now. What is the card and give your reasoning. |
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Subject: RE: BS: Logic puszzle From: jeffp Date: 07 Jul 05 - 03:29 PM Mr. P: I cannot tell which card it is. It must be A, Q, 4, or 5, the only ranks with duplicates. Mr. Q: I know you cannot tell. It must be hearts or diamonds, the only suits where all cards are duplicated in another suit. Mr. P: Based on what you just said, I know which card it is now. It cannot be the ace, since that is present in both hearts or diamonds. Mr. P knows the rank, since he was told. He now knows the suit because it is not one of the side suits. Mr. Q: Well, I also know which card it is now. This narrows it down to one card. The other one in the suit with only 2 cards, one of which is not duplicated in the other red suit. The card is the 5 of diamonds. I think. |
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Subject: RE: BS: Logic puszzle From: GUEST,MMario Date: 07 Jul 05 - 03:53 PM That's what I figgered Jeff. (and I got confirmation from the guy who sent it to me a couple minutes ago) You said it betteren then I did though. |
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Subject: RE: BS: Logic puszzle From: Ebbie Date: 07 Jul 05 - 03:57 PM Right. Bleahhhh |
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Subject: RE: BS: Logic puszzle From: GUEST Date: 07 Jul 05 - 04:00 PM Who cares? |
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Subject: RE: BS: Logic puszzle From: jeffp Date: 07 Jul 05 - 04:04 PM That was a pretty good exercise. Need to blow the cobwebs out of my brain once in a while. Thanks for posting it. Jeff |
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Subject: RE: BS: Logic puszzle From: GUEST,MMario Date: 07 Jul 05 - 04:06 PM What I hate about these kinda things Is I usually KNOW what the right answer is - then have to figure out HOW I know the answer. But the brain cell doesn't like having to do the extra work of going step by step - it LIKES shortcuts. |
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Subject: RE: BS: Logic puszzle From: JudyB Date: 07 Jul 05 - 04:23 PM Got there, with same general train of logic, but it took longer than I'd like - think I haven't stretched my brain this way for a while. Thanks! JudyB |
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Subject: RE: BS: Logic puszzle From: jeffp Date: 07 Jul 05 - 04:28 PM I had the wrong answer at first. Once I started writing it out, I realized that. It took a bit of figuring to come up with something I could justify. |
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Subject: RE: BS: Logic puszzle From: RobbieWilson Date: 07 Jul 05 - 06:22 PM This is not the only possible answer. The card could be 4 of Spades. Q knows because it is the only duplicate in the suit he has seen. He knows that P doesn't yet know because he knows it is a 4 and there is more than one 4. P knows once Q has told him he knows because Spades is the only suit where the 4 is the only possiblity. |
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Subject: RE: BS: Logic puszzle From: GUEST,Jon Date: 07 Jul 05 - 06:37 PM Interesting. Spades was the only suit I had eliminated. That to me would have prompted Q to say I know what card is in his first answer. I agree with Jeffp about the card values but I'm not following the eliminating clubs. By my way of thinking it doesn't matter that some clubs are not duplicated. P has said he can not tell what the card is. Q must know that P has eliminated the K and 6 of clubs. |
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Subject: RE: BS: Logic puszzle From: John Hardly Date: 07 Jul 05 - 07:48 PM "They know there are 16 cards in the drawer... AND they know what those 16 cards are. Sorry, but I couldn't make that assumption as the puzzle was written. I had to read jeff's answer and find that he had assumed it. |
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Subject: RE: BS: Logic puszzle From: Amos Date: 07 Jul 05 - 11:59 PM Beautifully done, Jeff. A |
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Subject: RE: BS: Logic puszzle From: dianavan Date: 08 Jul 05 - 12:16 AM keep those puzzles coming. Its good to exercise our brains that way. MMario - You sound like some of my students. They do not understand why they have to illustrate and explain their answers if the answer is right. Illustrating and explaining demonstrates cognitive understanding. The right answer proves only that you can calculate. These days, we have little machines that can do that. Whats needed today is not just higher level problem-solving skills but the ability to communicate that reasoning with others. BTW - I didn't get the right answer. In fact, I gave up. It was too hard for me. |
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Subject: RE: BS: Logic puszzle From: RobbieWilson Date: 08 Jul 05 - 11:18 AM Jon, it's true that spades might have prompted the response that you suggest from Q, but not neccessary. My solution does not make any of the statements untrue. You could rewrite the problem so that there was only the one solution if Q's first statement was " I already knew you could not tell which card it was" The reason clubs is eliminated is because if Q knew the suit was clubs it could have been the 6, in which case P would have known exactly which card it is because there was only one 6 among the 16. |
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Subject: RE: BS: Logic puszzle From: GUEST Date: 08 Jul 05 - 12:22 PM Dianavan - no, I do understand fully! I was lucky enough to have teachers who preferred that I got the WRONG answer with the correct procedure on test to giving the Correct answer with the wrong (or no) procedure. I'm just lazy. and of course - Seriously - I had one teacher who said he would have probably given me a zero on one test because it appeared to be a classic example of copying the answers from another - except A) I was the first person finished b) he had deliberately placed me in a location where not only couldn't I possibly copy from anyone else - but they couldn't copy from me. c) he already knew from previous work that I would often "jump" from one step to the next without working it out on paper - or even consciously. so he just made me redo it. and redo it. and redo it. until I had every single stupid step of every single problem on the entire friggin test written out on the paper. I got sick and tired of seeing that test paper come back with "missing steps" written across it. but I did learn a lesson. |
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Subject: RE: BS: Logic puszzle From: GUEST,Jon Date: 08 Jul 05 - 12:43 PM Thanks for the explanation and clarification, Robbie. Guest. I can't remember my teachers being specially worried whether we showed every step or not. We were warned though that it was in our own interests to show our workings. If say a question was worth 5 marks, a right answer would get 5 marks but a wrong answer with no working would get 0 marks. If the workings showed most of the steps right (eg, carrying through an error made in the first step), at least some marks could be awarded. |
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Subject: RE: BS: Logic puszzle From: dianavan Date: 08 Jul 05 - 12:44 PM The reason teachers do that is so that they can assess your understanding of the problem and the solution. Believe it or not, it would be far easier to just mark the answer right or wrong. You're actually lucky to have had teachers that cared enough to make you explain yourself. Its alot more work for the teacher. |
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Subject: RE: BS: Logic puszzle From: GUEST,MMario Date: 08 Jul 05 - 12:45 PM whoops! the lazy guest above was me. MMario |
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Subject: RE: BS: Logic puszzle From: Dave Hanson Date: 09 Jul 05 - 01:07 AM It's the jack of diamonds. eric |
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Subject: RE: BS: Logic puszzle From: Tam the man Date: 09 Jul 05 - 07:25 AM is it a card? |
