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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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Exactly what I thought, this "riddle" is going to die out...
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Should still work but may need to take quite a bit longer.
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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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I don't know... my LED bulbs would definitely fit the solution. It pains me to say, but I just checked.
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Agreed. But don't you think you gave it away, through your comment anyway?
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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.
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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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Our AI teacher on CS faculty gave us this assignment (and other of similar type about 15 years ago) to promote analog type of thinking ... meaning that not everything is about zeros and ones in computer science.
modified 19-Nov-18 21:01pm.
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Check the other rooms if their light go on/off?
"Program testing can be used to show the presence of bugs, but never to show their absence."
<< please vote!! >></div>
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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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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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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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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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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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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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What if you have an LED bulb in in the attic?
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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.
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Usually up is on such as decora, or the old switches were marked on and off.
Or take off the panel, and use a current meter to determine the on position, or volt meter or test light.
Turn all 3 switches on.
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Its so simple.. you turn ON ALL switches
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I'd say I'll use logic gates for this one. Not sure if it will be valid, don't care either if it is or not. 
Say we are talking about OR gates, we can have a single switch be turned differently from the other two switches. We will then have 1+0+0=1 or 1+1+0=1. Then the lamp is on.
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Assuming the bulb is incandescent and the switches are 1 -2 - 3
turn on switches 1 and 3 - wait 10 minutes - turn off switch three
go to the attic - if the light is on, switch one activates the lamp
if the light is off, feel the bulb
if it is warm, switch 3 activates the lamp
if it is cold, switch 2 activates the lamp.
SushiSlayer
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