# An Interview Question

#### Wallstyouth

##### Vice President
Ok so my friend told me about this silly question he was asked during an interview

You're in a room with 3 switches labeled A,B,C and across from that room is another room with 3 light bulbs not labeled, your allowed to go into the room with the bulbs once then you must return back to the room with the switches.

How can you accuratly figure out which switch coresponds with each light bulb.

Yes there is a solution but it takes a little bit of thinking out of the box.

Ill post the answer in 24 hours.

#### Andy Nguyen

Are we allowed to turn the switches on/off ?
If we are only allowed to look at the bulbs and then look at the switches without touching any of those, I don't see any way to figure out which switch belongs to which bulb (there are many if/else scenarios involved here). We must be able to change the states of the bulbs at least once each.

#### Wallstyouth

##### Vice President
Are we allowed to turn the switches on/off ?
If we are only allowed to look at the bulbs and then look at the switches without touching any of those, I don't see any way to figure out which switch belongs to which bulb (there are many if/else scenarios involved here). We must be able to change the states of the bulbs at least once each.

Yes you're allowed to turn switches on and off but remember you can only view the results once then you must return to the room with the switches.

#### Andy Nguyen

Am I allowed to touch the bulbs ?

#### Wallstyouth

##### Vice President
Am I allowed to touch the bulbs ?

Yes Andy looks like you figured it out

A dinner last night I was shocked how many people couldnt figure it out, I guess if you think too hard it can be difficult.

#### Adam

Yes Andy looks like you figured it out

The assumption, however, is that you're dealing with incandescent bulbs. Compact fluorescent bulbs don't generate heat, so this solution won't work if the room is eco-friendly. How's that for an inconvenient truth?

#### Andy Nguyen

The assumption, however, is that you're dealing with incandescent bulbs. Compact fluorescent bulbs don't generate heat, so this solution won't work if the room is eco-friendly.
With this kind of question, you can assume one thing and provide answer based on it.
That said, your statement is not entirely correct. Bulbs produce heat, not matter how little. Compact fluorescent bulbs generate much less heat than incandescent bulbs and it takes longer to warm up.
Howstuffworks "Are fluorescent bulbs really more efficient than normal light bulbs?"
So we can safely take several minutes to warm up our compact fluorescent bulbs so we can differentiate between off and on-then-off bulbs
How's that for an inconvenient truth?
Are you an Al Gore fan, Adam ?

#### goodstudent

I saw this question somewhere online, and one guy's answer was:

Turn one on, wait 1 million years, turn on the second one. Go in the room. The bulb thats broken goes with the first one. The one thats on goes with the second one. And the one that is off is the third.

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