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

  • question_answer
    A and B working separately can do a piece of work in 9 and 12 days respectively. If they work on alternate days beginning with A, then in how many days, the work will be completed?

    A)  \[11{\scriptstyle{}^{1}/{}_{4}}\]days               

    B)  \[5{\scriptstyle{}^{1}/{}_{4}}\] days

    C)  \[\text{9}{\scriptstyle{}^{1}/{}_{4}}\] days                  

    D)  \[\text{10}{\scriptstyle{}^{1}/{}_{4}}\] days

    Correct Answer: D

    Solution :

    (d) In 1 day, A completes \[\frac{1}{9}\]work In 1 day, B completes \[\frac{1}{12}\] work. If they work on alternate day, completion of work (till it gets fully completed) will follow the pattern:- \[\frac{1}{9}+\frac{1}{12}+\frac{1}{9}+\frac{1}{12}+.....\] now, \[\frac{7}{36}*5=\frac{35}{36}\] \[\Rightarrow \]In 10 days, \[\frac{35}{36}\] work will be over. \[\Rightarrow \]work left \[=1-\frac{35}{36}=\frac{1}{36}\] This A will able to complete in \[\frac{\frac{1}{36}}{\frac{1}{9}}=\frac{1}{4}\] days \[\Rightarrow \left( 10+\frac{1}{4} \right)\]days =\[10+\frac{1}{4}\]days.


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