Puzzle #3: Lightbulbs in the Attic

By Muriel Bristol (Transcriber) | September 11, 2018

One of many variants of the lightbulb puzzle:

There are three light switches downstairs. Each activates one of three lightbulbs in the attic. You can turn the switches on and off as much as you like and leave them in any position.

How can you tell which light switch corresponds to which lightbulb, if you are only allowed one trip upstairs?

[Answer to Puzzle #3 to follow in the next Puzzle]

Solution to Puzzle #2: Love in Kleptopia

Ms. Calderbrook’s own solution:

Jan sends Maria a box with the ring in it and one of his padlocks on it. Upon receipt Maria affixes her own padlock to box and mails it back with both padlocks on it. When Jan gets it he removes his padlock and sends the box back to Maria; voila! This solution is not just play; the idea is fundamental in Diffie-Hellman key exchange, an historic breakthrough in cryptography.

Other solutions are possible. One involved a second lock with a key small enough to fit inside the keyhole of a larger lock.

One of our commenters (Mike Sylvia) proposed a contemporary technological solution:

With the tip of the hat to Cody Wilson, I’ll take up a modern solution. Jan makes a scan of the key with which he padlocked the box. He e-mails the data file (encrypted, of course) to Maria. Maria uses her 3-D printer to reproduce the key to unlock the box when it arrives.

Yes, it seems like that would work too. It is not a perfect solution, in that it uses additional items, such as scanners and 3-D printers, not mentioned in the original puzzle. But, it is certainly novel and interesting.

Author: Muriel Bristol

"Lady drinking tea"

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