A two door gate of unknown width is opened so that a 2 ts'un gap exists between the two doors. It is known that the open door's edge protrudes 1 ch'ih from the door sill. What is the width of the gate? [Note: 1 ch'ih = 10 ts'un]
Jiuzhang Suanshu (The Nine Chapters on the Mathematical Art), c. 100 BCE
Click here to reveal the answer