In your cellar there are three light switches in the OFF position. Each switch controls 1 of 3 light bulbs on the floor above. You may move any of the switches but you may only go upstairs to inspect the bulbs once. How can you find the switch for each bulb with one inspection??
Flip switch number 1 and wait a few minutes. Flip switch number 1 back to its original position, and then immediately flip switch number 2.
Open the door. The light bulb which is on, belongs to switch number 2. Now go and feel the remaining two bulbs with your hand. The bulb that is hot, is connected to switch number 1 , and the bulb that is cold, is connected to switch number 3.
Come back next week for for our next riddle!