You are standing outside a room with no way of seeing what goes on in the room. Outside there are three switches turning on or off three lamps in the room.
Every switch is connected to only one lamp, and all lamps are now turned off.
Now you can turn on or off some of the lamps using the switches, open the door to the room, enter it, observe the situation in the room, and exit. Using this information you should determine how the switches are connected to the three lamps in the room.