【摘要】 回避数理统计中期望和方差的定义及性质，直接用排列知识和代数运算方法给出了抽样误差公式ｕｘ＝σ／ｎ的初等证明，使不具备数理统计知识的学生感觉简单易懂更多还原

【Abstract】 This article avoids the defintions and properities of expectations and variances in the methematical statistics by using the permutation knowledge and the mathod of algebraic operation and therefore comes the elementary proof of sampling errors formulas u x=σ/n.更多还原