Three signal lights flash at regular intervals. The Red light flashes every 2 seconds, the Green light every 3 seconds, and the Blue light every 4 seconds. If all three lights flash simultaneously at noon, how many seconds will pass before they all flash together again?
12 seconds
The time required for all lights to flash together is the Least Common Multiple (LCM) of 2, 3, and 4, which is 12 seconds.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Easy. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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