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Imagine a floodlight where each lightbulb is named from 1 to 100 The first guy turns every light on Similarly the second guy turns on (if its off) or off (if its on) every second lightbulb, 2,4, ... Similarly the third guy turns on (if its off) or off (if its on) every third lightbulb, 3,6, ... Now if this process is repeated till the 100th guy, which lightbulbs do you think will be still be ON ?

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