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    Question

    A and B can complete a work in 20 and 30 days,

    respectively. If they work together for 10 days and then A leaves, how many more days will B take to finish the work?
    A 5 days Correct Answer Incorrect Answer
    B 6 days Correct Answer Incorrect Answer
    C 7 days Correct Answer Incorrect Answer
    D 8 days Correct Answer Incorrect Answer
    E 9 days Correct Answer Incorrect Answer

    Solution

    A's work rate = 1/20 per day. B's work rate = 1/30 per day. Together, A and B’s combined work rate = 1/20 + 1/30 = 1/12 per day. In 10 days, they will complete: (1/12) × 10 = 5/6 of the work. Remaining work = 1 - 5/6 = 1/6. B alone can complete 1/30 of the work per day, so the time B will take to complete 1/6 of the work is: (1/6) ÷ (1/30) = 5 days. Correct option: a

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