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Math Help - mindblowing puzzle !!

  1. #1
    Newbie
    Joined
    Jun 2008
    Posts
    15

    Wink mindblowing puzzle !!

    Four people are on this side of the bridge. The bridge will be destroyed by a bomb in 17 minutes.
    Everyone has to get across before that.
    Problem is that :
    It's dark and they can't cross the bridge without a flashlight,
    They only have one flashlight.

    The bridge is only big enough for two people to cross at once.

    The four people walk at different speeds (specified below).

    When two people cross the bridge together (sharing the flashlight), they both walk at the slower
    person's pace.
    Can they all get across before the bridge blows up?
    person A: 1 minute
    person B: 2 minutes
    person C: 5 minutes
    person D:10 minutes

    Any soln for this ?????



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  2. #2
    Member
    Joined
    Sep 2007
    Posts
    75
    Highlight bellow for answer:

    Person A crosses with Person B (2 minutes),
    Person A crosses back alone and hands the flashlight to Persons C & D (1 minute),
    Person C crosses with Person D and hands the flashlight to Person B (10 minutes),
    Person B crosses (2 minutes),
    Persons A & B cross (2 minutes),
    17 minutes have elapsed (Person A and B's roles can be swapped as another solution).
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  3. #3
    Newbie
    Joined
    Jul 2008
    Posts
    5
    This is easy, just need to think just like the 3 missionaries and 3 canibals


    There has to be 1more missionary than the canibals, or they will eat the missionaries..

    So how can you transfer all the missionaries safe to the other side, only 3 in the boat per time.
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  4. #4
    Senior Member nikhil's Avatar
    Joined
    Jun 2008
    Posts
    292
    Quote Originally Posted by MathLearner View Post
    Four people are on this side of the bridge. The bridge will be destroyed by a bomb in 17 minutes.
    Everyone has to get across before that.
    Problem is that :
    
    It's dark and they can't cross the bridge without a flashlight,
    They only have one flashlight.

    
    The bridge is only big enough for two people to cross at once.

    
    The four people walk at different speeds (specified below).

    
    When two people cross the bridge together (sharing the flashlight), they both walk at the slower
    person's pace.
    Can they all get across before the bridge blows up?
    person A: 1 minute
    person B: 2 minutes
    person C: 5 minutes
    person D:10 minutes

    Any soln for this ?????



    For A,B,C and D to be saved they must cross the bridge befor or on 17 min
    first send A and B it will take 2 min.let B come back with light.it will take B 2 min to reach the initial point.so total time elapsed is 4 min.now send C and D with light it will take them 10 min.so far we have utilised 14 min.now Let A come back with light to take B them will take 1+2 min.
    So finally we have A,B,C and D at the end of the bridge in 17 min.
    Note if in the starting we had made A to back instead of B even then all of them would have made it in 17 min
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