Appendix: Solutions
Idea 1: Who owns the zebra?
This problem can be solved by analytical and logical thinking – deductive logic – and persistence! It is necessary to compile a matrix.
Roughly halfway through the problem-solving process there are two forks in the road, or mental leaps. The only way to find out which way to go is by trial and error. If you choose the wrong road, you have to retrace your steps. You can see now why the world record for finding the solution is 10 minutes!
The following is one way of solving the problem.
Keep working through the facts from 1 to 15 in sequence.
Concentrate on clues for which there is only one answer. That is:
1 There are five houses, each with a front door of a different colour, and inhabited by people of different nationalities, with different pets and drinks. Each person eats a different kind of food.
9 Milk is drunk in the middle house.
10 The Norwegian lives in the first house on the left.
15 The Norwegian lives next to the house with the blue door.
Then look for information that has only two possible answers. This is the first mental leap. That is:
6 The house with the green door is immediately to the right (your right) of the house with the ivory door.
If you place the ivory door in the middle, with the green door on its right, the answer is wrong, but you can still progress to find out who drinks the water. However, you can go no further.
If you place the ivory door in the fourth house, with the green door on the far right, this answer is correct and you can progress logically, since you will find that other items of information now have only one answer. That is:
2 The Australian lives in the house with the red door.
4 Coffee is drunk in the house with the green door.
8 Apples are eaten in the house with the yellow door.
12 Apples are eaten in the house next to the house where the horse is kept.
Then look for information that has only two possible answers. This is the second mental leap. That is:
3 The Italian owns the dog.
If you place the Italian in the house with the green door you are wrong, but you can still find out who drinks the water.
If you place the Italian in the house with the ivory door you are correct and you can progress logically, since you find that other items of information now have only one answer. That is:
5 The Ukrainian drinks tea.
13 The cake-eater drinks orange juice.
Therefore the Norwegian drinks water.
14 The Japanese eats bananas.
7 The mushroom-eater owns snails.
11 The person who eats onions lives in the house next to the person with the fox.
Therefore the Japanese owns the zebra.
Another way of solving this problem is to form a matrix using nationalities rather than house numbers:
