The Three Switches
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if the light is incandescent or halogen, it will get hot if left on. so switch on the first switch, and get distracted for 10 minutes, switch it off, switch on the next one and race upstairs. If the light is on, it is that 2nd switch. If it is off but hot, it was the first switch. Else it is the third switch. If it's an energy-efficient bulb, this won't work.
And we have a winner.
Wrong is evil and must be defeated. - Jeff Ello
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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...
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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.
Wrong is evil and must be defeated. - Jeff Ello
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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
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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.
Wrong is evil and must be defeated. - Jeff Ello
Firstly turn on switch1 for 1 minute, after 1 minute turn off the switch1, then turn on the switch2. go to the room and check the cases: case1: If bulb is on then switch2 is default switch. case2: Touch bulb by your hand if it is warm then switch1 is default switch. case3: If bulb is cold/normal then switch3 is default switch. default: No switch is working. ;)
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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
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
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if the light is incandescent or halogen, it will get hot if left on. so switch on the first switch, and get distracted for 10 minutes, switch it off, switch on the next one and race upstairs. If the light is on, it is that 2nd switch. If it is off but hot, it was the first switch. Else it is the third switch. If it's an energy-efficient bulb, this won't work.
Member 11762424 wrote:
If it's an energy-efficient bulb, this won't work.
Not necessarily true. Every bulb I have ever had has gotten hot - Incandescent, Fluorescent, and LED all produce heat. The latter two just produce less heat, so you need to run quicker.
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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
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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
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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.
Wrong is evil and must be defeated. - Jeff Ello
It's an analog solution, don't think in digital terms...unless you are well-versed in three-state logic. And yes the solution will work with CFL or LED bulbs, none of them are 100% efficient.
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Wouldn't work in this house: some of the switches are "top for off", others are "bottom for off"...:sigh: 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... :laugh:
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
The "correct" answer requires knowing when a switch is "on" or "off".
Truth, James
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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.
Wrong is evil and must be defeated. - Jeff Ello
The definite CORRECT solution (It's not the "official" solution) http://ericlippert.com/2011/02/14/what-would-feynman-do/[^]
Truth, James
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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.
Wrong is evil and must be defeated. - Jeff Ello
That was one of the three questions I was asked during an interview with a firm in Westlake Village. I got the job, so I guess I gave the answer that they wanted. Really, it's about common sense. The other question was to solve an equation for variables. It was perhaps solvable or not, but if you experimented by putting in some values, you figured out that any variables where y was x*2 and z was x*3 would work. I thought they were good tests. Common sense and problem solving.
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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.
Wrong is evil and must be defeated. - Jeff Ello
correct answer assuming all the switches are in the OFF position to begin with is, since you only can make one trip and you dont know which one it is. You turn them ALL on, and then can go. This is a waste of electricity but NOT a waste of time. so depending on the time frame, you can play with switches and guess/deduce with one it "probably" is but .... turning them ALL on, solves the puzzle. :)
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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.
Wrong is evil and must be defeated. - Jeff Ello
Okay, I had to think threw it a bit. Of course, my first reaction to the solution was my father yelling at me! And the hint is that you have to change 1 inspection to inspect for 2 potential details, to overcome the 3:1 input:output problem Nice puzzle
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Took me a couple minutes, but I remembered the answer... It's a nice warm-up problem... :)
Proud to have finally moved to the A-Ark. Which one are you in?
Author of the Guardians Saga (Sci-Fi/Fantasy novels) -
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
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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.
Wrong is evil and must be defeated. - Jeff Ello
Had this question at a job interview. It's a lateral thinking exercise. My experience with software development over 35 years is that lateral thinking is virtually never a part of the mental toolkit for software development. Oh, by the way, the solution requires that the bulb be an incandescent bulb. It won't work with an LED bulb or electroluminescent night light.
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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.
Wrong is evil and must be defeated. - Jeff Ello
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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.
Wrong is evil and must be defeated. - Jeff Ello
Here's my problem with the accepted solution -- How do you know that these aren't 3-way switches?? "One of them controls the lamp in the attic" -- which says nothing about whether the other two switches also control the lamp in the attic.
