Five light bulbs numbered 1 to 5 are all initially turned off. Switch 1 toggles bulb 1. Switch 2 toggles bulbs 1 and 2. Switch 3 toggles bulbs 1, 2, and 3, and so on up to Switch 5. If you flip Switch 2, then Switch 4, then Switch 5, which bulbs remain ON?
Bulbs 1, 2, and 5
Bulbs 1 and 2 are toggled by switches 2, 4, and 5 (3 times = ON). Bulbs 3 and 4 are toggled by switches 4 and 5 (2 times = OFF). Bulb 5 is toggled only by switch 5 (1 time = ON). Thus, bulbs 1, 2, and 5 are ON.
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: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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