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The Size of a City

A square walled city of unknown dimensions has four gates, one at the center of each side.  A tree stands 20 pu from the north gate.  One must walk 14 pu southward from the south gate, then turn west and walk 1775 pu before one can see the tree.  What are the dimensions of the city?

Jiuzhang Suanshu (The Nine Chapters on the Mathematical Art), c. 100 BCE

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"The Size of a City," Convergence (July 2006)