Switching On The Lateral Thinking
There are three switches outside a closed room. There are three lamps inside the room. You can flip the switches as much as you want while the door is closed, but then you must enter just once and determine which switch is connected to which lamp. How can you do it?
Switch the first one on for a minute, then turn it off and turn the second on. Enter the room and feel the two bulbs that are off. The warm one was turned on by the first switch, the light that is on is connected to the second, and the other to the third.