A large category of old chestnut is the logic puzzle of the type where you have N people, each of whom has a different favorite type of some thing (or other different properties), and you have several clues with which you need to match up the first and last names and their other properties.

Some puzzle magazines publish original puzzles of this type regularly, but one particular one that has circulated widely on the internet is the following, which is sometimes said to have stumped Albert Einstein, or to have been written by him.

There are five houses in a row on a street (which I will number one to five, left to right, for convenience). Each house is a different color, and each is owned by a man of a different nationality. Each owner drinks a different beverage, smokes a different brand of cigar, and keeps a different type of pet.

Clues:

  1. The Brit lives in a red house.
  2. The Swede keeps dogs as pets.
  3. The Dane drinks tea.
  4. The green house is on the immediate left of the white house.
  5. The green house owner drinks coffee.
  6. The owner who smokes Pall Mall, keeps birds.
  7. The owner of the yellow house smokes Dunhill.
  8. The owner of the third house drinks milk.
  9. The Norwegian lives in the first house.
  10. The owner who smokes Blend lives next to the one who keeps cats.
  11. The owner who keeps horses lives next to the one who smokes Dunhill.
  12. The owner who smokes Blue Master drinks beer.
  13. The German smokes Prince.
  14. The Norwegian lives next to the blue house.
  15. The man who smokes Blend has a neighbor who drinks water.
Whose pet is a fish?

For solving this problem, I suggest you use the grid elimination method described in The brakeman, the fireman, and the engineer. You might arrange the variables like this:

          houses  color  drink  cigar  pet
nat'lity     X      X      X      X     X
pet          X      X      X      X
cigar        X      X      X
drink        X      X
color        X

Where each X represents a five-by-five grid in which you can represent the relations between the five values of the two variables.

Answer

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