Sunday, November 24, 2013

A Classic Logic Puzzle: Who Owns The Fish?

There are five houses in a row and in five different colors.

In each house lives a person from a different country.

Each person drinks a certain drink, plays a certain sport, and keeps a certain pet.

No two people drink the same drink, play the same sport, or keep the same pet.

1.      The Brit lives in a red house
2.      The Swede keeps dogs
3.      The Dane drinks tea
4.      The green house is on the left of the white house
5.      The green house owner drinks coffee
6.      The person who plays polo rears birds
7.      The owner of the yellow house plays hockey
8.      The man living in the house in the center drinks milk
9.      The Norwegian lives in the first house
10.  The man who plays baseball lives next to the man who keeps cats
11.  The man who keeps horses lives next to the one who plays hockey
12.  The man who plays billiards drinks beer
13.  The German plays soccer
14.  The Norwegian lives next to the blue house
15.  The man who plays baseball has a neighbor who drinks water.

So to solve this on you own, don’t read further. Otherwise, follow along below.

First draw five boxes in a row, to represent the houses.
Then put down the basic stuff we know without other information. This includes 8, 9, and by deduction from 9, 14.
Next we know from 4 and 5, that the furthest right house must be the white house with the green to its left. It can’t be shifted over any, due to the prohibition of the middle house drinking milk.

Now we can figure out the next two colors from 1. Since the Norwegian lives in the first house, it can’t be red, and is yellow by default.
We can now, knowing the yellow house, complete 7 and 11, since 11 can apply to only one house. 
This is the tricky step. Based upon a couple of clues we need to do some guesswork. We know the Swede can only live in one of two places, and the Dane can only live in one of two places, based on 2, 3, and 13.

If we consider further clues 12 and 15, then it is a pretty safe bet that the Dane lives in the blue. You can of course reverse this, but in the next step you’ll find logical inconsistencies. We now need to figure out which is German and Swedish.
 Like the last step, we can make a choice. If we say the Swede is in the green house, we run into problems in the next step with clue 12. If we assume the contrary, we are presented with no difficulties.

We can plug in 12, and 15 now safely.

By default, clue 6 must be the middle house, and we can safely say from 15 that the Dane plays baseball.
Clues 10, and for dramatic flair, 2 (which we could’ve done earlier) can now be figured out.

Finally we have our answer:

1 comment:

Karen said...

I LOVE logic puzzles! Thanks for this one.