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

  • question_answer
    A pipe can fill a tank in 15 hours. Due to leak in the bottom, it is filled in 20 hours. If the tank is full, how much time will the leak take to empty ti ?

    A)  120 hours                    

    B)  80 hours        

    C)  40 hours          

    D)  60 hours

    Correct Answer: D

    Solution :

    (d): Filling in 1 hr \[=\frac{1}{15}\]tank Let emptying by leak in 1 hr = \[\frac{1}{x}\]tank (where leak empties tank in 'x' hrs) \[\therefore \]Hrs in which it fills along with leak also emptying \[\Rightarrow \frac{1}{\frac{1}{15}-\frac{1}{x}}\] = 20hrs \[\Rightarrow \frac{1}{15}-\frac{1}{x}=\frac{1}{20}\] \[\Rightarrow \frac{1}{x}=\frac{1}{15}-\frac{1}{20}=\frac{5}{30}=\frac{1}{60}\] x = 60 hrs.


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