Simple maths problem, did I do it right?

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  1. #1
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    Simple maths problem, did I do it right?

    I had this problem on a test. I failed it there due to lack of time, but I still want to know if I can solve it. Did I do it right?

    Code:
    Pump 1 pumps up the oil in a tank in 24 H. Pump 2 pumps up the oil in 36 H. How many H does it take to pump up the oil if both of the pumps are working?
        
            
        
                  
            /----\
            Work        
       /-------------\
      /Capacity|H     \
     /-----------------\
    
    After 100 units of work, the oil has been pumped up.
    
    Work/Pump1 H = Pymp 1 Capacity
    100/24 = 4,167
    
    Work/Pump2 H = Pump 2 Capacity
    100/36 = 2,778
    
    Pump 1 Capacity+Pump 2 Capacity
    4,167+2,778 = 6,945
    
    Work/Capacity = H
    100/6,945 ~= 14,4
    
    4*0,6=2,4
    
    
    Result: 14 H and 24 min
    Last edited by Zewu; 10-20-2002 at 12:55 PM.

  2. #2
    S Sang-drax's Avatar
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    Let me see...

    Tank volume : 1 v.u.

    Pump1 speed : 1/24 v.u./h
    Pump2 speed : 1/36 v.u./h

    Total speed : 1/24 + 1/36 = 5/72 v.u./h

    Combined time = (1 v.u.) / (5/72 v.u./h) = 14.4 h = 14 hours 24 min

    Correct!
    Last edited by Sang-drax : Tomorrow at 02:21 AM. Reason: Time travelling

  3. #3
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    Yet another solution

    V is the volume of tank

    P1 pumps up V/24 oil per hour

    P2 pumps up V/36 oil per hour

    If they would work together they pumped up V/24 + V/36 oil per hour

    They will work V/(V/24 + V/36) hours to make the tank full

    that is V / (V * (36 + 24) / 36 * 24) = 36 * 24 / (36 + 24) =

    14,4 hours = 14 h 24 min

    Don't you have any tougher?

  4. #4
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    Sorry, but I'm in grade 9 of our social democratic compulsory school. They don't want those who appear to have an easy time with, for example maths, to get their own tougher questions, test, teachers etc., as this would create an elite.
    Last edited by Zewu; 10-21-2002 at 01:15 PM.

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