Light the Bulbs Puzzle
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There are 100 bulbs in a room. 100 strangers have been accumulated in the adjacent room. The first one goes and lights up every bulb. The second one goes and switches off all the even-numbered bulbs – second, fourth, sixth… and so on. The third one goes and reverses the current position of every third bulb (third, sixth, ninth? and so on.) i.e. if the bulb is lit, he switches it off and if the bulb is off, he switches it on. All the 100 strangers progress similarly.
After the last person has done what he wanted, which bulbs will be lit and which ones will be switched off? 
1,4,9,16,25,36,49,64,81,100 will be lit only
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