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    Question

    A alone can complete a work in 10 days and B alone can

    complete it in 15 days. They work together for 5 days and then C alone finishes the remaining work in 2 days. In how many days can C alone complete the whole work?
    A 25 days Correct Answer Incorrect Answer
    B 18 days Correct Answer Incorrect Answer
    C 12 days Correct Answer Incorrect Answer
    D 15 days Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    A's 1-day work = 1/10 B's 1-day work = 1/15 (A + B)'s 1-day work = 1/10 + 1/15 = (3 + 2)/30 = 1/6 Work done in 5 days by A and B = 5 × 1/6 = 5/6 Remaining work = 1 − 5/6 = 1/6 C does 1/6 work in 2 days C's 1-day work = (1/6) ÷ 2 = 1/12 So C alone can finish full work in 12 days. 

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