Mary, Jane, and Lucy are typing a manuscript and are capable of completing the whole manuscript in $${2}\frac{1}{2}$$ hours if they work together. If Mary alone can type the same manuscript in 10 hours, and Jane is capable of typing the complete manuscript in 6 hours, in how many hours can Lucy type the whole manuscript?
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A$${1}\frac{1}{5}$$
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B$${2}\frac{1}{7}$$
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C3
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D5
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E$${7}\frac{1}{2}$$
显示答案
正确答案: E