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9th Class Mathematics Related to Competitive Exam Question Bank Arithmetic

  • question_answer
    Two fill pipes A and B can fill a cistern in 12 and 16 minutes respectively. Both fill pipes are opened together, but 4 minutes before the cistern is full, one pipe A is closed. How much time will the cistern take to fill?

    A) \[9\frac{1}{7}\] minutes      

    B)        \[3\frac{1}{3}\] minutes

    C) 5 minutes            

    D)        \[3\,\] minutes

    E) None of these

    Correct Answer: A

    Solution :

    Explanation Option [a] is correct. Let cistern will be full in x min. Then, part filled by B in x min + part filled by A in (x ? 4) min = 1 \[\Rightarrow \,\frac{x}{16}+\frac{x-4}{12}=1\] \[\Rightarrow \,x+\frac{64}{7}=9\frac{1}{7}\min .\]


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