$\"\"$

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The value of tract of timber is $\"\"$ , where $\"\"$ is time in years.

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$\"\"$ corresponding to $\"\"$ .

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Money earns interest continuously at $\"\"$ .

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The present value of the timber at any time $\"\"$ is $\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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$\"\"$

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Differentiate the above equation with respect to $\"\"$ .

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$\"\"$

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Equate $\"\"$ to zero to find the year in which the timber is harvasted to maximum profit.

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$\"\"$

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$\"\"$ , $\"\"$

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$\"\"$

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The year in which the timber is harvasted to maximum profit is $\"\"$ .

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$\"\"$

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The year in which the timber is harvasted to maximum profit is $\"\"$ .