|
Downstairs in a house are three identical on-off switches.
One of them controls the lamp in the attic.
The puzzle is to work out which switch controls the lamp.
The rules are as follows.
You are allowed to manipulate the switches all you like, and then you are allowed a single trip to the attic.
How do you do it?
To clarify: When you are downstairs there is no way to see into the attic, or see reflected light from the attic.
Once you have gone to the attic you are not allowed back to the switches.
<edit>you can also assume original state of all switches to be off.</edit><hint>Otherwise it won't work</hint>
Note: If you already know the answer, or reads the newspaper where I nicked the puzzle from, then please don’t write it up immediately in the comments!
Give those who have never heard it before a chance to suffer, I mean enjoy finding the solution.
modified 7-Jul-15 16:54pm.
|
|
|
|
|
Two ways I can think of:
1) Look at the effect of each switch on other lights in the house. The one that doesn't have any effect is the attic one (or a bulb is blown)
2) Send the wife up to the attic and tell her to yell when the light goes on!
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
|
|
|
|
|
Those are practical solutions, not adjusted for silly puzzles. My wife wouldn't go up to the attic in any case.
|
|
|
|
|
I'm a practical person! 
Jörgen Andersson wrote: My wife wouldn't go up to the attic in any case.
Too many spiders?
(Can't stand the venomous little buggers, myself)
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
|
|
|
|
|
Mice traps, or rather the reason for them.
|
|
|
|
|
Yup, same goes to my wife, she wont do it in any case 
|
|
|
|
|
OriginalGriff wrote: Send the wife up to the attic and tell her to yell when the light goes on!
Once you lose your pride the rest is easy.
In the end, only three things matter: how much you loved, how gently you lived, and how gracefully you let go of things not meant for you. – Buddha
|
|
|
|
|
- Turn all the switches off;
- Go to the attic;
- Remove the bulb from the lamp;
The correct answer is now "none of them". 
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
|
|
|
|
|
Wouldn't work in this house: some of the switches are "top for off", others are "bottom for off"...
One of these days I'll sort it out, but I'm afraid the writing won't take changes and I don't want to have to redecorate...
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
|
|
|
|
|
Well, he didn't state top or bottom, he stated off.
|
|
|
|
|
If you don't know what they control, you don't know which way is on... 
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
|
|
|
|
|
OriginalGriff wrote: If you don't know what they control, you don't know which way is on
So if you know that they control a lamp in the attic... 
|
|
|
|
|
The "correct" answer requires knowing when a switch is "on" or "off".
Truth,
James
|
|
|
|
|
Do you know, before you start flipping switches, whether the light is already on?
|
|
|
|
|
|
Took me a couple minutes, but I remembered the answer... It's a nice warm-up problem...
|
|
|
|
|
|
What's the purpose of going to the attic if you cannot go back to the switches afterward?
The difficult we do right away...
...the impossible takes slightly longer.
|
|
|
|
|
I send a drone to the attic with a camera so I can see which switch switches the light on.
|
|
|
|
|
The classic solution (which I won't give away) may not work too well with modern LED globes! CFLs maybe.
Cheers,
Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
|
|
|
|
|
Exactly what I thought, this "riddle" is going to die out...
|
|
|
|
|
Should still work but may need to take quite a bit longer.
|
|
|
|
|
CFLs still get hot enough to the touch that you don't want to replace them immediately after they fail. LED's are only marginally more efficient; half of the "bulb" ends up being a heat sink. Bean counters being what they are; I'd expect it to be the bare minimum size required and to still get nice and warm.
Did you ever see history portrayed as an old man with a wise brow and pulseless heart, waging all things in the balance of reason?
Is not rather the genius of history like an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful?
--Zachris Topelius
Training a telescope on one’s own belly button will only reveal lint. You like that? You go right on staring at it. I prefer looking at galaxies.
-- Sarah Hoyt
|
|
|
|
|
I don't know... my LED bulbs would definitely fit the solution. It pains me to say, but I just checked.
|
|
|
|
|
Agreed. But don't you think you gave it away, through your comment anyway?
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
