You are standing outside the first floor entrance to a building.

Next to you is a bank of 3 light switches.

One of the switches controls a light bulb in a stock room on the second floor.

The other two switches don't control anything.

The only way you can check the light on the second floor stock room is to physically walk up the stairs, open the door to the stock room, and check the light.

You can do anything to the switches that you want before you walk up the stairs, however you are allowed only one trip up the stairs to check the light.

Assuming the light and switches are off to start with, how do you find out which light switch controls the light using only one trip to the room?

Read the quiz and take little time to think. Give your feedback then see the right answer.

Answer

Turn on the first switch, wait for a couple of minutes to allow light bolb to get hot, and then turn off the first switch and turn on the second switch. Go to the second floor immediately and if the light bolb is off but hot, it's the first switch. If the light is on, it's the second switch. If the light is off and cool, it's the third switch.