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Railways Sample Paper RRB (Group D) Sample Test Paper-7

  • question_answer
    If A and B together can complete a piece of work in 15 days and B alone in 20 days, in how many days can A alone complete the work ?

    A)  60                   

    B)  45

    C)  40                   

    D)  30

    Correct Answer: A

    Solution :

    [a] (A+B)'s 1 day's work =\[\frac{1}{15}\] B's 1 day's work = \[\frac{1}{20}\] \[\therefore \]A's l day?s work \[=\frac{1}{15}-\,\frac{1}{20}=\frac{4-3}{60}=\frac{1}{60}\] \[\therefore \]A alone will do the work in 60 days Alternate Method: Work efficiency of A + B: working efficiency of \[B=\frac{1}{Time\,of(A+b)}:\frac{1}{Time\,of\,B}=\frac{1}{15}:\frac{1}{20}=4:3\] Total work unit = efficiency of worker \[\times \] time of worker \[=15\times 4=60\] efficiency of \[A=4-\,3=1\] Required time \[=\frac{60}{1}=60\]days


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