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Brain Teaser: Who Owns the Fish?

Posted by Cliff on from the just-for-fun dept.

So I was looking for something new and different to do for this weekend's Ask Slashdot. Lo and behold mallocat submits a logic problem! "I wanted to try and use the Slashdot effect to attack this brainteaser. A couple of my friends and I each sepeartely solved it in about an hour..." that's the time to beat, but I'm giving you all till midnight Sunday to figure it out, and then I'll post the solution on Monday in forum. It's simple: First person to solve the problem (determined by timestamp of comment submission), with proof, wins. Winner gets a hearty, virtual slap on the back. I'd offer more, but since I have no budget, that makes it rather problematic. <grin!> So without further ado, click on that link! Albert Einstein wrote this riddle. He was quoted saying that he believed that 98% of the world could not solve it. Are you in the top 2% of intelligent people in the world? There is no trick-just pure logic.

Good luck.

  1. There are 5 houses in 5 different colors, all in a row.
  2. In each house lives a different person with a different nationality.
  3. These 5 people drink a certain type of beverage, smoke a certain brand of cigar, and keep a certain pet.
  4. No person has the same pet, smoke the same brand of cigar, or drink the same beverage.
  5. The Brit lives in the Red house.
  6. The Swede has a dog.
  7. The Dane drinks tea.
  8. The Green house is on the left of the White house.
  9. The Green house's owner drinks coffee.
  10. The person who smokes Pall Mall has a bird.
  11. The owner of the Yellow house smokes Dunhill.
  12. The man living in the center house drinks milk.
  13. The Norwegian lives in the first house.
  14. The man who smokes Blends lives next to the cat owner.
  15. The man who owns a horse lives next to the one who smokes Dunhill.
  16. The man who smokes BlueMaster drinks beer.
  17. The Berman Smokes Prince.
  18. The Norwegian lives next to the Blue House.
  19. The man who smokes Blends has a neighbor who drinks water.
Who owns the Fish?

21 comments

  1. Who owns the fish? by guenth · · Score: 1

    The Berman owns the fish, lives in a green house,drinks coffee, and smokes prince.

    1. Re:Who owns the fish? by Clifton+Wood · · Score: 1

      Errr... Now the big question is: HOW did you manage to reply to the comment before it was posted?

    2. Re:Who owns the fish? by guenth · · Score: 1

      Very good question. :-)
      I wasn't paying real close attention to the time when I posted. I just noticed that there weren't any other comments posted at the time. Something got apparently got stamped wrong...

  2. Who owns the fish by ShadeTC · · Score: 1

    The berman owns the fish.

    Proof at: http://www.wpi.edu/~tcollins/riddle.pdf

    tc

  3. ok.. by Zurk · · Score: 1

    heres another one :
    FIRE and TORN make one word when combined. what is it ?

  4. 98% could not solve it? by Chacham · · Score: 1

    *Could* not solve it, or *would* not?

    I actually do not like this style of riddle. It never really interested me. The logic I love, but the listing of rules just rubs me the wrong way.

    Here's a few for you. The first can be solved with simple math. The second has something incorrect, and the third is logic.

    A warning on the second, it has driven people crazy. I have only met one person who got the answer within seconds, and I do not think that he is smarter than the average bear. He just listened carefully, I guess.

    1) A donkey and a mule were each carrying some packages. The donkey groaned. The mule, hearing the groan, asked the donkey rhetorically, "Why do you groan? If I were to give you one of my packages, we would be carrying the same amount, and if you gave me one of your packages I would then have double what you have!".

    How much was each animal carrying?

    2) Three people were on a business trip and needed to stay the night. Towards the evening they started to look for a room to rent. After a shortwhile they came accross a motel.

    They entered the motel and asked the owner how much a room was for one night. He told them that thirty dollars would do it. So each one coughed up ten bucks, and off they went to their room.

    A little while later the owner felt bad for he had overcharged them by five dollars. The room was only twenty five dollars a night. So, he got ahold of the bellboy, gave him five dollars, and asked him to give it back to them.

    They bellboy, realizing that they each split the room, began to wonder how to split five dollars amongst three people. After a bit of thought he came up with a very simple solution. He gave one dollar back to each guy and pocketed the other two.

    OK, story's over. But let's figure something out. Each guy paid ten dollars originally and got one dollar back, which means that they ended up paying nine dollars apiece for the room. Being they were three people, that is a total of twenty seven dollars. Let us not forget that the bellboy pocketed two dollars. Adding that to the total gives twenty nine dollars.

    Where is the remaining dollar?

    3) Three boys were playing on the beach, and all got mud on their forheads without knowning it. An older gentleman walked over to them and asked them to each take a look at both their friend's foreheads. And then, if either one, or both, had mud on their foreheads, they should raise their hand. Each one looked at both their friends, and then each raised their hand.

    The older gentleman now asked a second question, and offered a dollar to whomever could prove their answer. The question was, "Without touching your own forehead, do you have mud on your own forehead?".

    The three stood silently for a while, none could figure out the answer. Finally one raised his hand and said, "I have mud on my forehead." The man asked him how he knew, and he proceeded to give a proof. The man was satisfied and gave him the dollar.

    What was the proof?

    --
    Have you read my journal today?
    1. Re:98% could not solve it? by dvdbn · · Score: 1

      Answer to #1: 7 & 5. It can be solved quite easily by two equations: 1) x-1=y+1 and 2) x+1=2(y-1). Solve the first for x: x=y+2. Now plug into the second equation: y+2+1=2(y-1). Simplify: y+3=2y-2, which becomes y+5=2y. Easy to solve from there.

      Answer to #2: You don't add it to find the total, you subtract it. 3*9=27, minus the two the bellboy stole = 25, which is the total for the room. That's how it works. I read carefully and got that, not too hard but it'll confuse most people.

      I'd be curious to hear the answer to #3. I'd bet that you screwed up the wording somewhere because think of it like this: "if either one, or both, had mud on their foreheads, they should raise their hand." Boy #1 knows that both Boy #2 and Boy #3 have mud on their heads. He knows that Boy #2 knows that Boy #3 has mud on his head AND the condition of Boy #1's head. Boy #1 also knows that Boy #3 knows that Boy #2 has mud AND the state of Boy #1's head. Boy #1 raises his hand because both others have mud on their heads. Boy #2 raises his hand because Boy #3 has mud on his head, but what about Boy #1? "either one, or both..." Same deal with Boy #3. Switch around the numbers any way you like, none of them can know (just by pure logic) whether or not they mud on their head. Or at least that's my contention.

    2. Re:98% could not solve it? by Chacham · · Score: 1

      You answered number one and two very well. You are on the right track for number three. You are correct that statement is important, to some degree. Here is a hint. The most impotant thing is "The three stood silently for a while, none could figure out the answer.". That's what tipped me off when I read the question in some book. This one actually took me a few minutes to figure out. You'll enjoy it when you figure it out.

      The second one was asked to me when I was in grade school, by an after-school math program teacher. While I knew what was wrong, I didn't know why. And it took years until I actually thought about it and figured it out. :-)

      --
      Have you read my journal today?
  5. 26 minutes.... by dvdbn · · Score: 2

    good god. alright i spent a total of 26 minutes on this and this is what i came up with.

    going from left to right....

    House #1
    -Yellow
    -Norwegian
    -Dunhill
    -Cat
    -Water

    House #2
    -Blue
    -Dane
    -Blends
    -Horse
    -Tea

    House #3 (center)
    -Red
    -Brit
    -Pall Mall
    -Bird
    -Milk

    House #4
    -Green
    -Berman
    -Prince
    -Fish
    -Coffee

    House #5
    -White
    -Swede
    -BlueMaster
    -Dog
    -Beer

    i went over it three times and everything works out. so the Berman has the fish. hope that's right.

  6. Times have changed . . . by Hadji · · Score: 1

    I would guess that Einstein's estimation that only 2% of the world's population could solve this is no longer true. I would venture to say that there are many more multitudes of people today who are trained in logic.

    I learned the method for solving these types of logic puzzles when I was in grade school (I am now 30). If you know the method, it's not nearly as challenging as Einstein's estimation implies.

  7. It's obvious to me now . . . by Hadji · · Score: 1

    If all three raised their hand to the first question, then at least two boys had to have mud on their foreheads. If either boy saw a forehead free of mud, then it would be obvious that he had mud on his own forehead and he would not hesitate to answer the old man's second question.

    But when one boy noticed the other two being silent, he surmised that he must have mud on his own forehead.

    1. Re:It's obvious to me now . . . by Chacham · · Score: 1

      Excellent. You absolutely right. Now don't you feel good all over. :-)

      --
      Have you read my journal today?
  8. That was one heck of a hint . . . by Hadji · · Score: 1

    After you gave it away, it was easy. :-)

    1. Re:That was one heck of a hint . . . by Anonymous Coward · · Score: 0

      This is Chacham, not logging in because of the computer that I am on. I can verify later when I get home if needed. :-) Always, always, use reverse logic. It is one of the best methods. I like to say that everything is defined by its opposite. Basically, if something had no opposite, it would be everything. Therefore, if something is not clear, look at its opposite. It's enough to make you flip your bits. :-). This question actually took me five minutes to figure out. Easy once I realized how to figure it out. BTW, did I give away the hint to quickly? I just wanted to answer the earlier comment that I didn't give enough information. I figured that if you didn;t want a hint, you should not have read further. :-)

    2. Re:That was one heck of a hint . . . by Hadji · · Score: 1

      Actually, I needed the hint. I went through all the possible combinations, as stated in someone elses previous comment, and it didn't make sense to me as to how the boy could prove it. I knew there was something I was missing, but I had no idea what it was, and it was driving me nuts.

      When I read your hint, it was like some guy in a clown suit had crashed through my window and bopped me in the head with a barrage of snurf missles with each missile having the answer written on it in black permanent marker.

      And the clown was singing, in his best Janis Joplin impression, "THIS IS WHAT YOU'RE MISSING!!"

    3. Re:That was one heck of a hint . . . by Chacham · · Score: 1

      :-)

      Glad I could be of service.

      What I have found, however, is that when you figure out the answer yourself, as you did, you thoroughly enjoy this problem. WHen someone tells you the answer, you may think it is dumb.

      Try it on a few friends. See what they think.

      --
      Have you read my journal today?
  9. What is the method to solve this ? by Etyenne · · Score: 1

    I tinkered on the problem for about half an hour. My method was to aggregate known data (the green house resident drink coffee and live next to the white house) in the hope that all would fall in place by itself. Unfortunately, I ended up with only two three-variable aggregate :

    - the green house resident drink coffee and live next to the white house.

    - the norwegian live in the first house and is the neighboor of the blue house.

    With so little correlated data, I think it is impossible to just deduce the outcome as a succession of logical step. IMHO, you have to think of all the possibilitie and test them against the 15 rules. Since I am a lazy butt, I did'nt bother to "brute force" the solution.

    There should be 375 000 possibilities : 5e5 (5 variables : pet, nationalitie, beverage, cigarette and house color) * 5! (possible house position). It should be (relatively) easy to build a data structure in Perl that would represent all these possibilitie, and code the rule to test them against. The tricky part would be to represent the house position. Being the lazy butt I am, I did'nt to code it, but that might be an interesting challenge for the next time I'll have to much time on my hand.

    Anyway, I might be wrong : there might be a way to deduce the solution without testing all the possibilitie. What do you think of that ?

    --
    :wq
    1. Re:What is the method to solve this ? by Anonymous Coward · · Score: 0
      Anyway, I might be wrong : there might be a way to deduce the solution without testing all the possibilitie. What do you think of that ?

      Well, at least there is already a kind of language specially designed to implement half-brute-force search of such solutions: Prolog. I wanted to try this with the language Mercury on my machine, but for some reason, their authors insist on doing general purpose programming with it, so there is not a single example of code, or document about how to use predicate programming. I'll try when I get a Prolog interpreter wih examples.

  10. The method was best demonstrated by ShadeTC by Hadji · · Score: 1

    I do believe that the method to solve this was best demonstrated in a previous comment by ShadeTC. In his comment, he posted a URL to his proof.

    The idea is to make such a chart as he's made, and as you read through the clues, X out what is impossible, mark an O for what is possible. You have to go through the rules over and over again. As you go through the process of elimination, certain correlations start falling into place revealing the possibilities and impossibilities of other correlations.

    Check out ShadeTC's url:
    http://www.wpi.edu/~tcollins/riddle.pdf

    1. Re:The method was best demonstrated by ShadeTC by dvdbn · · Score: 1

      I sat down with two pieces of paper and a pen. first i wrote down all of the facts, then i turned my music up loud so nothing else would interrupt me. as i went through the facts, i started linking things together, what is and what isn't possible. i remembered that there was a chart method to do it after i had completed it. would go down the list and write down, for instance: "blue house - doesn't drink water, milk or coffee, drinks tea or beer" and then determined it was tea. like i said, i got it done in 26 minutes, but i was working extra fast to beat the 1 hour "time to beat" :) the second piece of paper i used to draw 5 boxes representing the houses, and when i was absolutely SURE of something (norwegian lives in the first house, etc.) wrote it down under the house. it was easier for me to put it all together like that. your mileage may vary. just my input for solving problems like this.

  11. Re:answer..dont read if you havent solved it. by Zurk · · Score: 1

    FRONTIER