Riddle: Their are three fully functioning light bulbs in a room hanging from the ceiling. You are in an adjacent room with no windows and three switches on the wall. You must find out which switch goes to which bulb. The rules, you can only flip two switches at a time and go and look at the bulbs. You may then turn off the switches and go back to the bulbs. After that, you can no longer look at the bulbs or touch the switches.
Answer: Flip two switches and leave them on for a few muinets and go look at the bulbs. Then, flip off one switch and leave the other one on for a minuite or so more. Then go look at the bulbs. The hottest on is the last switch to be turned off, and the next hottest on it the second to last switch you turned off.