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Question
Mohan takes 9 hours to mow a large lawn. He and Sohan together can mow it in 4 hours. How long will Sohan take to mow the lawn if he works alone?
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Solution
\[\text{ Time taken by Mohan to do the work = 9 hours} \]
\[\text{ Time taken by Mohan and Sohan to do the work = 4 hours } \]
\[ \therefore \text{ Work done by Mohan } = \frac{1}{9}\]
\[\text{ Work done by Mohan and Sohan } = \frac{1}{4}\]
\[ \therefore \text{ Work done by Sohan } = \frac{1}{4} - \frac{1}{9}\]
\[ = \frac{9 - 4}{36} = \frac{5}{36}\]
\[\text{ Thus, Sohan can do the work in } \frac{36}{5} \text{ hours i . e } . 7\frac{1}{5}\text{ hours } .\]
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