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The Old Switch-A-Roo

Logic puzzles require you to think. You will have to be logical in your reasoning.


Puzzle ID:#40504
Fun:*** (2.82)
Difficulty:** (1.73)
Submitted By:niveknedarbus




Stan is applying for a job with a high paying electrician known to hire people who can think outside of the box. He tells Stan that if he can solve a particular problem, he will get the job. The boss puts Stan outside the door to a room from which light cannot escape. Inside the room is a lamp. On the wall next to Stan are four switches, one of which works the lamp, the other three do nothing. Stan needs to figure out which switch works the lamp, but the boss has taken away all of his tools. He has told Stan that he may flip the switches to his heart's content, but he can only open the door to examine the lamp once. What should Stan do with the switches to ensure he gets the job?

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Feb 14, 2008

Excellent teaser but I have one thing to say about it... what if the light was on to begin with????
Feb 14, 2008

I thought:
Turn on 1 & 2, let sit awhile.
Then, turn off 2 and on 3 (leave 1 on) and open door and quickly go in.
light is on and hot, it was 1
light is off and hot, it was 2
light is on but not yet hot, it was 3
light is off and cold, it was 4
Feb 14, 2008

I have the same answer as the previous poster. It's a better solution to the teaser because it doesn't require you to differentiate between "hot" and "warm". In the sense of a logic teaser it offers a more elegant solution, imho.
Feb 15, 2008

Cheeny has an excellent point, but I still think it's pretty clever as it is.
Feb 16, 2008

I agree with the others who have commented. What if the light was already on? You should have stated that at the beginning i think. I enjoyed the teaser though, even if i solved it with relative ease.
Feb 17, 2008

sorry folks I should have stated that both the lamp and all the switches were off to begin with.This was my first teaser,I'll try harder next time
Feb 17, 2008

My thought was that the rules didn't say Stan had to determine the switch before he opened the door. All he had to do was open it and start flipping switches till the lamp came on.
(user deleted)
Feb 28, 2008

Flip all of the light switches at the same time and open the door. The correct switch is still flipped. The other three do nothing so they're moot.
Mar 05, 2008

sorry sunshine if it were that easy the hire powers would not have accepted it
Mar 20, 2009

I had the same solution as xdbtpc and tpg76. Whether the light was on or off to begin with doesn't matter as long as you wait long enough with switches 1 and 2 on.

Clever teaser though. I actually had to look at the hint to get this one, and I almost never read the hints. Not sure how well this works with compact florescent light bulbs.
Jun 06, 2009

If three of the switches do nothing as it says then you would only have a 50% chance of finding the switch that works the light upon entering the room the first time. You could if you alter this problem figure out which switch lights the light if allowed to enter the room twice. How you ask? Flip your best guess switch and wait a few minutes. Turn it off and take a guess on another switch by turning it on and entering the room. If it's on it was the second switch you choose. If it is off hope the bulb is warm when you touch it and you can say it is the first switch you picked and you were lucky. Thus a 50% chance of impressing your new boss. If you failed to guess right the first time then repeat the procedure above with the other two switches since one of them is the working switch.

Now had there only been three switches two that don't work it is possible to say which switch work on one trip. Do you know how?????
I do.
Jun 06, 2009

I forgot to mention it does matter whether the light is on or off unless the bulb is warm or on when you enter. It could have cooled in the time you allowed for it to warm. So I guess we need to ask our boss to be certain questions to clarify the problem before starting. It would also matter if the switches were upside down as to on and off. We can never assume in a logic situation.
Nov 03, 2012

Excellent teaser. Very clever. Only one complaint from me: the way it's worded -"he can only open the door to examine the lamp once" - the situation allows for him to simply open the door once and LEAVE IT OPEN, in which case the solution is very very easy.

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