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# Bulbs

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There are three switches downstairs. Each corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position.

How would you identify which switch corresponds to which light bulb, if you are only allowed one trip upstairs?

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Bulbs - solution

Keep the first bulb switched on for a few minutes. It gets warm, right? So all you have to do then is ... switch it off, switch another one on, walk into the room with bulbs, touch them and tell which one was switched on as the first one (the warm one) and the others can be easily identified ...

This is one of my favorite logic puzzles (Edit: it is more a practical than a logic puzzle).

Imagine you are in a room with 3 switches. In an adjacent room there are 3 bulbs (Edit: let's say in lamps which are on a regular table) - all are off at the moment, each switch belongs to one bulb. It is impossible to see from one room to another. How can you find out which switch belongs to which bulb, if you may enter the room with the bulbs only once?

Edit: No help from anybody else is allowed.

Edit: Find out which switch belongs to which bulb - identify all 3 switches (so find out what bulbs are switches 1, 2 and 3 connected to)

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• 3 weeks later...
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I don't think LED bulbs get discernibly warm.

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Turn on all the switches and you'll know what color all the bulbs are.

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You only need to turn on 1 switch as each switch belongs to one bulb. That one bulb will come on no matter which switch you turn on.

Regards

kolonel

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Assuming that there is some sort of doorway/passageway between the rooms, and that the rooms are next to each other (and also assuming that the bulbs are not arranged in a straight line as observed from that doorway).....then you can tell which bulb is on by simply observing the shadow is being cast through the doorway by the bulb. Maybe this is personal...but walking into the room and touching a HOT bulb that has just been turned off does not sound like much fun to me.

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Maybe this is personal...but walking into the room and touching a HOT bulb that has just been turned off does not sound like much fun to me.

that is not personal...

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Alternatively:

-1 switch off = bulb off

-1 switch on = bulb on

-1 switch halfway (yes you can do this) = bulb dim & flickering

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You could also walk into the room and have someone else turn on/off each switch. It never said you couldn't recruit help.

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There is a little problem in the way that the puzzle is introduced.

You say that this is one of your favorite "logic" puzzles.

But the minute I read "logic" and your "favorite" it brought out the big guns. I worked on a purely logical solution for almost 2 weeks and obviously there isn't one because the solution is a prctical solution not a "logical" one.

Now, I know that all puzzles are logic testers but to label a puzzle a "logic" puzzle is to suggest that the solution is not worldly.

I want my 2 weeks back. lol

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Walk into the other room and remove all bulbs. Now you know that none of the switches is connected to any bulb.

Alternately, you could disconnect the switches, put batteries of specific voltages on each wire, then test each socket to see which one is connected to which battery.

I agree that "logic puzzle" and "touch the warm bulb" seem a little not synonymous, but I want to thank you for this, because I used this trick to troubleshoot my brake lights (it's hard to view the bulb while sitting in the car pressing the brake pedal). I could have wedged something between the brake pedal and the seat, but I figured this would be easy enough, and it worked.

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Sounds logical to me!

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If you could label this puzzle one of two ways:

A "practical" puzzle or

a "logic" puzzle

which do you think would be most appropriate?

All I am trying to say is that solving some puzzles doesn't involve sensing and touching.

(it's no big deal, I don't really want my 2 weeks back)

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ok so if you can only walk into the room once, than how can you eaisly determine the other two, you can only turn on one light switch or you wont be able to figure out the other two because two lights will be hot and will not be able to tell which switch is which.

help me figure this one out.

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ok so never mind i got it.

i got temperarily confused.

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I would hire a new electrician......one who is better at planning and mapping out the switches and receptacles, so it wouldn't be necessary to turn on a light from three rooms away.

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• 3 weeks later...

This is the original puzzle (which rookie1ja adapted):

There is a room with a door (closed) and three light bulbs. Outside the room there are three switches, connected to the bulbs. You may manipulate the switches as you wish, but once you open the door you can't change them. Identify each switch with its bulb.

Notice the closed door. No looking into the room, looking at shadows, etc.

The only way to do it is to turn one on for some time, switch it off, turn on another switch, and walk into the room. The one that's on is connected to the switch you just turned on, the bulb that's hot is the one you turned on first, and the cool bulb is connected to the switch you didn't touch.

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Could you just plant them?

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Could you just plant them?

They're light bulbs, not flower bulbs ><

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here is a good solution... turn on 2 random switches... open the door to the other room... break 1 of the bulbs... go back to the switch room.... while looking at the door to the other room... turn one of the switches off... if the light goes you now know all 3... if it doesnt go out... you still know all 3

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Well, "logic" puzzles mean that you have to think about it using logic, not necessarily meaning that it's solution must be logical.

Well, I've found another way to solve this puzzle, but it's almost the exact same as the one you are all presenting.

Turn on two of the switches, wait some time, turn one of them off, go in.

The one the is on should be obvious, the one that you just turned off would be the one that is off but hot, and the cold one is the one you never touched.

The solution you provided is:

Turn on one switch, wait, then turn that one off, turn on another one, then walk in. Repeat the remaining steps from the previous example.

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but I want to thank you for this, because I used this trick to troubleshoot my brake lights (it's hard to view the bulb while sitting in the car pressing the brake pedal). I could have wedged something between the brake pedal and the seat, but I figured this would be easy enough, and it worked.

Dude, back your car into your driveway at night and look for the brake light glare against your garage door in the rear view mirror.

I don't object to the use of the term "logic," but most rooms I've been in you can't just reach up and touch a light bulb. Your premises were incomplete as they did not mention the light bulbs were in arm's reach (or are you using a ladder in the other room? Or a hot air balloon? You don't even tell us how you reach them).

An equaly good solution is to walk into the room and use your magic lightswich identifier box. ...Oops, sorry, did I forget to mention you had one of those?

It's kinda like that.

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Turn two of the three switches on. wait some time, turn one of them off. The switch that stays on will match the light that is on - the switch that was left off will match the cooler of the two off bulbs and the last switch that was turned on for some time and then turned off will be warmer than the other bulb that is off.

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ok, are these switches in my kitchen? because I have at least one switch that I really think the previous owners put there as a cruel joke. maybe they wired to a light at their new place that illuminates the word "SUCKER" every time I flip it.

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Turn on the first switch and then wait a few minutes.

Then turn it off and turn on the second switch right away and wait a few minutes.

Now turn off the second switch and walk into the other room.

Touch all of the bulbs and feel for which bulb is the hottest. This one is with the second switch.

The cooler, but still warm bulb is with the first switch.

The coolest bulb is the third switch.

The bulb with the first switch isnt the hottest becuz it had time to cool down while the 2nd switch's bulb was still hot.

YOU FOOLS SHOULDN'T HAVE WASTED 2 WEEKS ON THIS; IT DOESN'T TAKE THAT LONG TO FIGURE OUT THIS SIMPLE PROBLEM!

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YOU FOOLS SHOULDN'T HAVE WASTED 2 WEEKS ON THIS; IT DOESN'T TAKE THAT LONG TO FIGURE OUT THIS SIMPLE PROBLEM!

Are you on stilts? How do you propose to touch the light bulbs? You make it sound simple in 1, 2, 3 instructions, but like I said, you could just as easily say:

1. Turn on one bulb, wait several minutes.

2. Turn off the first switch, and turn another one on.

3. Quickly walk into the room and pull out your magic switch detector to achieve the answer.

Neither reachable bulbs, nor a magic detector box is mentioned in the premises, so both are equally valid (IE invalid) when introduced at the conclusion.

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