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13/12/2017 at 16:35
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Pump P can fill a water tank in 12 hours, and Pump Q can fill the same tank in 15 hours. The two pumps started filling the tank at the same time and worked together until the tank was 60% full. At that point, Pump P was turned off, and Pump Q continued to fill the tank until it was completely full. How many hours did it take to completely fill the tank?



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    Nguyễn Hưng Phát 13/12/2017 at 17:42

    A hour Pump Q can fill a water is:

               \(1:15=\dfrac{1}{15}\)(tank)

    A hour Pump P can fill a water is:

            \(1:12=\dfrac{1}{12}\)(tank)

    A hour Pump P and Pump Q can fill a water is:

        \(\dfrac{1}{12}+\dfrac{1}{15}=\dfrac{3}{20}\)(tank)

    The time for Pump P and Pump Q fill 60% full is:

       \(\dfrac{3}{5}:\dfrac{3}{20}=4\)(hours)

    The time for Pump Q fill 40% full is:

             \(\dfrac{2}{5}:\dfrac{1}{15}=6\)(hours)

    The number of hour for it take to completely fill the tank is:

       6+4=10(hours)

    Answer:10 hours

      

        

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    KEITA FC 8C 19/12/2017 at 12:48

    A hour Pump Q can fill a water is:

               1:15=1151:15=115(tank)

    A hour Pump P can fill a water is:

            1:12=1121:12=112(tank)

    A hour Pump P and Pump Q can fill a water is:

        112+115=320112+115=320(tank)

    The time for Pump P and Pump Q fill 60% full is:

       35:320=435:320=4(hours)

    The time for Pump Q fill 40% full is:

             25:115=625:115=6(hours)

    The number of hour for it take to completely fill the tank is:

       6+4=10(hours)

    Answer:10 hours



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