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Thread: Pls solve this Aptitude Question????

  1. #1
    Join Date
    Aug 2007
    Posts
    2

    Default Pls solve this Aptitude Question????

    Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins.If all of them work together, find the time taken to fill the tank???
    1)17 1/7 MINS
    2)20 MINS
    3)8 MINS

    pls explain in detail

  2. #2
    Join Date
    Aug 2007
    Posts
    1

    Default

    Let x = no. of minutes to fill the tank.

    Equation:
    x/20 + x/30 - x/40 = 1
    6x/120 + 4x/120 - 3x/120 = 1
    7x/120 = 1
    7x = 1 * 120
    x = 120/7
    x = 17 1/7

    The answer is 1) 17 1/7 MINS

  3. #3
    Join Date
    Aug 2007
    Posts
    1

    Default

    Let the volume of tank be V
    A can fill tank in 20 min => In 1 min A can fill up v/20 of the tank

    lly

    B can fill tank in 30 min => In 1 min B can fill up v/30 of the tank

    lly

    C can empty tank in 40 min =>In 1 min C can empty v/40 of the tank

    Let t be the time taken for the tank to be completly filled i,e Volume V

    => volume filled by A in t min + volume filled by B in t min +
    volume emptied by c in t min = V
    => t(V/20)+t(V/30)+t(-V/40) = V
    => tV(1/20+1/30-1/40)= V
    => t= 120 / 7
    = 17 1/7

  4. #4
    Join Date
    Aug 2007
    Posts
    1

    Default

    its 1 - 17 +(1/7)

  5. #5
    Join Date
    Jun 2009
    Posts
    1

    Default explanation

    Quote Originally Posted by rakesh View Post
    Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins.If all of them work together, find the time taken to fill the tank???
    1)17 1/7 MINS
    2)20 MINS
    3)8 MINS

    pls explain in detail
    1/20+1/30-1/40=7/120.... inverse of it is 120/7 that is 17 1/7 mins..

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