Amongst my Christmas presents was a book, “Einstein’s riddle, paradoxes, puzzles and conundrums” by Jeremy Stangroom. One of the first puzzles in the book is this logic problem, attributed (almost certainly incorrectly) to a young Einstein:
There are 5 houses painted in 5 different colours. A person with a different nationality lives in each house. The 5 owners each drink a certain type of beverage, play a certain sport and keep a certain pet. No owners have the same pet, play the same sport or drink the same beverage.
- The Briton lives in the red house.
- The Swede keeps dogs as pets.
- The Dane drinks tea.
- The green house is immediately[1] on the left of the white house.
- The owner of the green house drinks coffee.
- The person who plays football rears birds.
- The owner of the yellow house plays baseball.
- The man living in the centre house drinks milk.
- The Norwegian lives in the first house.
- The man who plays volleyball lives next to the one who keeps cats.
- The man who keeps the horse lives next to the man who plays baseball.
- The owner who plays tennis drinks beer.
- The German plays hockey.
- The Norwegian lives next to the blue house.
- The man who plays volleyball has a neighbour who drinks water.
Who owns the fish?
Whatever its origins, it is a cracking puzzle. It took me the best part of an hour to solve it. If your brain is under-stimulated from Christmas TV but you are forbidden from programming, I recommend you give it a go. The answer is here (no peeking!).
Normal service will be resumed on this blog soon.
[1] See Atul’s comment below.
Successful Software 
I’ve seen this puzzle before and wanted time to have a crack at it. It took me about an hour and I used a spreadsheet, where I made a grid and filled in the ‘must be correct’ items one at a time, duplicating the grid and making notes each time I made a change.
I enjoyed it and would recommend having a go if you enjoy logic problems such as Sudoku. It’s not difficult, but will require a quiet mind for a stress-free – and therefore enjoyable – experience.
My favourite feature of the puzzle is the little trap you have to avoid, which I can’t really describe here without spoiling it, but I will say that you have to be careful not to imply your own meanings. I saw the trap, smiled to myself, then forgot and fell for it later on.
Atul commented:
“I solved the puzzle but come up with a different solution. I noticed no contradictions in my solution, so I followed the link to the wikipedia article and found the following with reference to statement 4 (The green house in on the left of the white house.)
“It is also important to note that the omission of the word immediately, as in immediately to the left/right of the white house, leads to multiple solutions to the puzzle.”
So either you should edit the puzzle to include immediately or edit your solution and mention that multiple solutions are possible.”
I had assumed it meant immediately to the left. I have now added the word *immediately* to avoid any ambiguity.
Great! Thanks for reading my comment.
Doh, glad I checked back here… Atul’s clarification made all the difference in figuring this out.
That was great fun. Makes me want more.
Wow. Got it. It is an addiction.
I cracked it in 5 seconds. It is insoluble. There is no evidence that anybody keeps a fish.
Maybe the fifth pet is a hamster, a goat, unicorn…
Perhaps I should assume that there is indeed a fish. That would make it more interesting. :-)
Enjoyable brain teaser, but the clarification regarding wether the green house is to the immediate left of the white actually gave me another clue, and after I realized that it only took me a couple of minutes to finish the puzzle.
I read through the list and, assuming it was a trick question (e.g. What color was George Washington’s white horse?), came to the same conclusion as Shraddhan.
Shraddhan, JGarrido:
The fact that someone keeps a fish is implied in the text of the question.
Rik, following that logic, that’s kind of like saying every question has an answer that can be found following deductive reasoning. However, none of the known facts even came close to implying ownership, by anyone, of a fish. And process of elimination can only be used with facts.
The question cannot create its own answer.
If you study the question carefully, you should see that the final sentence reads ‘Who owns the fish?’
This question gives you the information that the final and, indeed, most important pet is a fish.
So I’m not saying that _every_ question has an answer that can be found following deductive reasoning. Only that this one can – by reading the question.
I think I’ve just been burned one too many times to be able to agree to make that assumption; the wording of the question is just a bit too ambiguous the way it stands. Had the author of the puzzle wanted to leave no doubt, they would have worded it with more clarity – by stating the remaining pet was a fish and asking who owned it; or by listing every nationality, drink, sport, and pet individually before getting into the known associations.
But then why bother naming the pet at all? Why not just ask who owned the remaining ‘unmentioned’ pet? It can’t be assumed that the question contains any relevant information.
The pet is named so that you have something to write in the empty space in the grid you will likely create. Or just to spare us the terrible sense of incompleteness that may be felt with the final pet’s species left unresolved.
I think it’s fair to distribute the information needed to answer the question throughout the text of the question.
I thought the statement “The Norwegian lives in the first house,” was rather ambiguous. Is that the first house on the left or the first house on the right?