《九章算术》是我国现存最早的数学专著.它的第八章《方程》的第13题是著名的“五家共井”问题,题是这样的:“今有五家共井,甲二绠不足如乙一绠,乙三绠不足如丙一绠,丙四绠不足如丁一绠,丁五绠不足如戊一绠,戊六绠不足如甲一绠.如各得所不足一绠,皆逮.问井深、绠长各几何?”(题中:“绠”是汲水桶上的绳索,“逮”是到达井底水面的意思.) The “Nine Chapters of Arithmetic” is the earliest existing mathematical monograph in China. Its Chapter 13 of the “Equation” in Chapter 13 is the famous “Five Wells” problem. The title is: “There are five common Wells, A deficiency, such as B one, B three defects such as C one, C four deficiency is not enough as a Ding Yi, D is less than five, such as E, Yiwu lack of such as A Yi. Such as the respective Less than a moment, all are arrested. Ask the well depth and length of each geometry? (”In the title: “ 绠 ”is the rope on the bucket, “ catch ” is to reach the bottom of the water surface meaning.)