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Thread: Puzzle for 100 Bulbs

  1. #1
    Junior Member
    Join Date
    Jun 2011

    Exclamation Puzzle for 100 Bulbs

    College has two rooms, one is having 100 bulbs and other room has its switches. Switches doesn't have number/name written on it. New warden doesn't know the switches for the bulbs. How many trips he has to make to identify all the switches for the bulbs?

  2. #2
    Expert Member
    Join Date
    Jun 2006

    Re: Puzzle for 100 Bulbs

    He can do it in 20 trips...

    Here is my solution,
    1. Group 100 switches in to group of 10 each.
    2. On all the switch in one group, make a trip and note down the bulbs belong to the group
    3. Repeat step 2 for all the groups . That will make 10 trips and at the end bulbs also grouped along with switches.
    4. Now on one switch per group - 10 switches are on now
    5. make a visit and mark down the bulbs - each bulb is matched with its switch
    6. Repeat step 4 and 5 - for remaining 90 bulbs

    so by end of this 20 trips he will be able to match all 100 switches with its bulbs

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