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    Question

    A and B can jointly finish a task in 42 days, while B

    and C together take 35 days to finish the same task. If B can finish the task alone in 105 days, how long would it take for A and C to complete the task together?
    A 28 days Correct Answer Incorrect Answer
    B 32 days Correct Answer Incorrect Answer
    C 30 days Correct Answer Incorrect Answer
    D 25 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let total work = 210 units (LCM of 42, 35 and105) Amount of work done by A and B together in one day = 210/42 = 5 units Amount of work done by B and C together in one day = 210/35 = 6 units Amount of work done by B in one day = 210/105 = 2 units Amount of work done by A in one day = 5 – 2 = 3 units Amount of work done by C in one day = 6 – 2 = 4 units Desired time = 210/(4 + 3) = 30 days

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