Wednesday, September 04, 2013

Who Owns the Zebra?

I collect problem-solving methods. A recent letter from a follower give me the chance to show you another method I often use on the problems that bother me most. It's especially helpful with problems I'm having with other people. Here's the letter and my response:

Who Owns the Zebra? It was the first difficult logic puzzle I solved. I saw it in a Reader’s Digest once when I was waiting for a haircut at a barber shop. And of course it was back when cigarettes were considered cool (but not Kool, what my parents smoked – yuck!). I was around 8 years old at them time.

For your convenience, here's the puzzle from this website:

On a city block there are five houses in a row, numbered from left to right, each of a different color and inhabited by men of different nationalities, with different pets, drinks and cigarettes. You are given the following clues:
  • The Englishman lives in the red house;
  • The Spaniard owns the dog;
  • Coffee is drunk in the green house;
  • The Ukrainian drinks tea;
  • The green house is immediately to the right of the ivory house;
  • The Old Gold smoker owns snails;
  • Kools are smoked in the yellow house;
  • Milk is drunk in house #3;
  • The Norwegian lives in house #1;
  • The man who smokes Chesterfields lives in the house next to the man with the fox;
  • Kools are smoked in the house next to the house where the horse is kept;
  • The Lucky Strike smoker drinks orange juice;
  • The Japanese smokes Parliaments;
  • The Norwegian lives next to the blue house;

Now, who drinks water? And who owns the zebra?
I remember reading this puzzle in the International Edition of Life Magazine, back in 1962.
If you'd like to see an interactive Windows program that can generate thousands of puzzles like this, take a look at Everett Kaser's SHERLOCK program.
I give up, show me the solution.

Since most of the people in the puzzle were smokers in 1962, the zebra puzzle is now easy to solve, using one of my favorite methods--the 50-year approach:

1. Put the puzzle in an envelope. Write on the envelope: "Do not open until [50 years from today]."

2. When the 50 years have passed, open the envelope. Chances are that it will no longer be a problem.

3. If, however, it's still a problem, get another envelope and repeat step 1. 

4. By the time you open envelope #2, the problem will be solved for you. It will no longer be a problem. I guarantee it.