This is a gem of a puzzle – read it this morning in the book Mathematical Puzzles and Diversions by Martin Gardner. I have had many of the Martin Gardner books for ages now, but overtime I open these books, I continue to find hidden treasures there!
An electrician is faced with this annoying dilemma. In the basement of a three-storey house, he finds bunched together in a hole in the wall the exposed ends of 11 wires, all alike. In a hole in the wall on the top floor, he finds the other ends of the same 11 wires, but he has no way of knowing which end above belongs to which end below. His problem: to match ends.
To accomplish his task, he can do two things:
- Short circuit the wires at either spot by twisting the ends together in any manner he wishes
- test for a closed circuit by means of a “continuity tester” consisting of a battery and a bell. The bell rings when the instrument is applied to the two ends of a continuous, unbroken circuit.
Not wishing to exhaust himself by needless stair climbing, and having a passionate interest in solving puzzles (like all of you!), the electrician sat down on the top floor with a pencil and paper and soon devised the most efficient possible method of labelling the wires.
What was the method?
As always, please send your answers as comments within the blog (preferred), or send an e-mail to email@example.com. Please do share the puzzle with others if you like, and please also send puzzles that you have come across that you think I can share in this blog.