three lights on top floor. three switches on ground floor. find out which switch belongs to which light with fewer trips to top floor. no other twists involved in the words. you know the routine. this is one of the oldest puzzles that i know.

click here for answer

switch on any two lights
after few mins, switch off one of them
go upstairs
light which is still burning belongs to switch that is on
light bulb which is cool and off belongs to switch that was never turned on
light bulb which is hot and off belongs to switch that was turned on then off.