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Difficult Brain Twister

Difficult Brain Twister - 28 October

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 progresses in the similar fashion.

After the last person has done what he wanted, which bulbs will be lit and which ones will be switched off ?

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  1. Replies
    1. What will the 4 th person do ? Turn on everything?

  2. 1,4,9,16,25,36,49,64,81,100 on rest off

  3. The 100th person will have the first persons job-mathematically- 3/99+33 changes, so the 34th (100 person) change is starting over at #1, which is to turn them all on.

    1. Should say 3 / 99 = 33 the 34th change is starting over.

  4. Only perfect squares will be lit (1,9,16,25,36,49,64,81 & 100), rest will be switched off.