>>>>>Nope. Actually this one is much simpler than yours was if you think about it...
>>>>I think I got it.
>>>>Turn one switch on and leave it on, long enough for the light bulb to heat up.
>>>>Turn off that light, and turn on another just before you enter the room.
>>>
>>>Yep :) I knew this one from the times, I was a kid...
>>
>>Have you heard this one?
>>
>>You have 12 billiard balls.
>>
>>One of them is either lighter or heavier than the others.
>>
>>You can weigh the billiard balls 3 times on a balance scale.
>>
>>You need to find out which ball it is and whether it is heaver or lighter.
>>
>>Is this possible?
>
>I could not make it in my mind. Tried few combinations unsuccessfully. I think, 3 times are not enough...
>
>BTW, have you heard, that the Great Ferma theorem is solved? I don't have link handy at the moment...

It is possible. You have to divide the balls into 3 groups of four balls each. And then you should label each group A, B, and C. That gets you started.

I've never heard of Great Ferma theorem. What is it?