This is a very famous puzzle, allegedly invented by Albert Einstein as a boy, and reputedly the hardest puzzle in the world. It is said only 2% of people can solve it. There is no trickery involved, all that is required is appliance of logic to build up the complete picture from the supplied information, which then answers the puzzle.
There are five houses painted different colours, and a person of different nationality lives in each house. The five owners each drink a different beverage, play a different sport and own a different pet.
- The Briton lives in the red house
- The Swede keeps a dog
- The Dane drinks tea
- The green house is on the left of the white house
- The green house's owner drinks coffee
- The footballer owns a bird
- The yellow house's owner plays baseball
- The person in the middle house drinks milk
- The Norwegian lives in the first house
- The volleyball player lives next to the cat owner
- The horse owner lives next to the baseball player
- The tennis player drinks beer
- The German plays hockey
- The Norwegian lives next to the blue house
- The volleyball player's neighbour drinks water
Who owns the fish?
The best approach is to create a grid with house numbers across the top and Features (such as Pet or Nationality) down the side, and then use the facts to fill in the grid.
From Fact 9 the Norwegian lives in the leftmost house.
And from Fact 8 Milk is drunk in the middle house.
Then Fact 14 means that house two (next to the Norwegian) is Blue.
From Fact 5 we can see the Green house can't be house three as the owner doesn't drink milk. And from Fact 4 we can see it is on the left of another house that is White. The only place for the Green house is number 4, and house 5 is then white. Coffee is drunk in house 4.
From Fact 1 the Briton's Red house can't be number 1 (as that's inhabited by a Norwegian), so he must live in house number 3.
Yellow is now the only colour left for house number 1.
Then Fact 7 shows that the baseball player is in (the Yellow) house number 1.
And then Fact 11 gives the horse owner in house number 2, next to the baseball player.
Fact 12 informs us that the tennis player drinks beer. He can't be British (drinks Milk) or Norwegian (plays Baseball); Fact 3 shows he can't be Danish (drinks Tea) and Fact 13 shows he can't be German (plays Hockey). So he must be Swedish and from Fact 2 we know he keeps dogs.
This can fit in house number 5 only.
From Fact 3, the tea-drinking Dane can live in house number 2 only.
And the German must be in house number 4.
And we already know the German plays Hockey from Fact 13.
The only place for the water drinker is house number 1.
Fact 15 gives the Volleyball player in house number 2.
And then the footballer is in house number 3, and Fact 6 shows he owns birds.
Fact 10 gives the cat owner in house number 1.
And we have one space left for the Fish fancier to live in house number 4.
The fish is owned by the German.