A little teaser I guess I messed up on.

[Zeke]

Here's a little brain teaser from the Net. I don't know if it's proprietary to where I found it, but I'll let it remain anonymous for the time being unless I get flak.

"Brainteaser

You are working in a building and have a problem. On the top floor are three standing lights. On the ground floor are three switches, which control the lights, presently all in the "off position. You don't know which switch controls which light, except that there is a one-to-one correspondence. You're down on the ground floor and want to label the switches. But you want
to do it in as few trips up stairs as possible.


The room the lights are in can only be seen from the top floor (it has no windows and its at the end of a long corridor.) There's no one around to help. You must do it alone.

What is the fewest trips you can make to determine which switch turns on which light? You may assume that the bulbs have just been replaced, all the wiring is good, etc."

OK, here's how I thought I solved it.
" Turn on 2 lights, go upstairs and determine which of the 3 is not lit. Return to ground floor, label the appropriate switch and switch off 1 of the first 2. Back to upstairs to eliminate which one and you have it."

I got a response from the "author" that I got no prize.

Do me better then, One trip? I need to know how that works. NO trips? Well, color me stupid.

[Eric Coffey]

Turn 1st switch on, and leave on.
Turn 2nd switch on for a while, then turn off.
Run upstairs to check lights.
Lit bulb = 1st switch.
Unlit but warm-to-touch bulb = 2nd switch.
Unlit and cold bulb = 3rd switch.

[pwd72s]

Place two mirrors at the top of the stairs...

[Zeke]

Originally Posted by Eric Coffey

Turn 1st switch on, and leave on.
Turn 2nd switch on for a while, then turn off.
Run upstairs to check lights.
Lit bulb = 1st switch.
Unlit but warm-to-touch bulb = 2nd switch.
Unlit and cold bulb = 3rd switch.

You get the prize. I guess I should have paid more attention to the "standing lights" part. I assumed you couldn't touch them.

Good job.

[bell]

I was going to say just label them 1,2, and 3 without going upstairs......I mean who the hell wired that place where the switches would be so far away? LOL

[Zeke]

Originally Posted by bell

I was going to say just label them 1,2, and 3 without going upstairs......I mean who the hell wired that place where the switches would be so far away? LOL

Same thought here, but I bit for the tease. Obviously I took the mechanical approach and not the scientific (analytical) one.

Wait unit island911 sees this. I'm done with a fork in me.