Interview Question for Product Analyst at Stockamp & Associates:

Start with all the switches in the off position. Turn on two of the three switches. when you enter the room the first time, if the light is off, then you know it is the switch you didn't turn on. Else, turn on that switch and turn off one of the switches you previously had on. Now, if the light is off when you enter the room, you know it is the switch you just turned off. If the light is on, you know it is the switch that you had turned on when you looked at the room the first time.