Light in room riddle
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You are standing in front of a room with one light bulb inside of room. You cannot see whether it is on or off. Outside the room there are three switches in the off positions. You may turn the switches any way you want to. You stop turning the switches, enter the room and know which switch controls the light bulb. How? 
On button 1 wait for few minutes for the bulb to become hot if it gets on, then switch it off and then on button 2 and enter room immediately.
If light is on then 2 is the button
If light is off, touch the bulb. If it is hot then 1 is the button if it is cold, then 3 is the button
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