How many bulbs will light up?-2.(correct) version

Level 2

I have got 100 lamp bulbs with 100 switches. Initially all switches are turned off. After that I change the position of each switch. After that I change the position of each second, third, fourth... hundredth switch. How many bulbs will light up?


The answer is 10.

A Former Brilliant Member by A Former Brilliant Member

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1 solution

The lights on will be the numbers having an odd number of factors. These are the ones which are perfect squares: 1 , 4 , 9 , 16 , 25 , 36 , 49 , 64 , 81 , 100 1,4,9,16,25,36,49,64,81,100 Total = 10 \text{Total}=10

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