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    Question

    Varun and Arnav can finish a work in 28 days and 56 days

    respectively when working alone. Varun starts first. In how many days should Arnav join him so that the entire job finishes in 21 days?
    A 6 Correct Answer Incorrect Answer
    B 5 Correct Answer Incorrect Answer
    C 7 Correct Answer Incorrect Answer
    D 10 Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the total work be 56 units (LCM of 28 and 56)

    Efficiency of Varun = (56 / 28) = 2 units/day

    Efficiency of Arnav = (56 / 56) = 1 unit/day

    Let Arnav join after 'n' days.

    So, 2n + (2 + 1) × (21 - n) = 56

    ⇒ 2n + 63 - 3n = 56

    ⇒ n = 7

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