一般地,对于n个数$x_{1}, x_{2}, \cdots,x_{n}$,我们把$\frac{1}{n}($$x_{1},+x_{2}, \cdots+x_{n})$叫做这n个数的,简称,记作$\bar{x}$.
一般地,若有n个数$x_{1},x_{2}, \cdots,x_{n}$的权分别是$w_{1},w_{2}, \cdots,w_{n}$,则$\frac{x_{1} w_{1}+x_{2} w_{2}+\cdots+x_{n} w_{n}}{w_{1}+w_{2}+\cdots+w_{n}}$ 叫做这n个数的.