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8th Class Mathematics Direct and Inverse Proportions Question Bank Direct & Inverse Proportional (Time & Work)

  • question_answer
    Two pipes A and B can fill a tank in 2 hours and 75 minutes respectively. There is also an outlet C. If all the three pipes are opened together then the tank is full in 50 minutes. How much time will be taken by C alone to empty the full tank?

    A)  90 minutes      

    B)  10 hours

    C)  150 minutes                 

    D)  120 minutes

    Correct Answer: B

    Solution :

    (b): 2 hrs =120 min Let 'C' empty in 'X' minutes Time taken when all are open together = 50. \[\therefore 50=\frac{1}{\frac{1}{120}+\frac{1}{75}-\frac{1}{x}}\] \[\Rightarrow \frac{1}{x}=\frac{1}{120}+\frac{1}{75}=\frac{5+8-12}{600}=\frac{1}{600}\] \[x=600\text{ }min=10hrs.\]


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