Mathematical variance formula: S2 =1/n [(x1-m) 2+(x2-m) 2+. +(xn-m) 2]。 Variance formula is a mathematical formula and an important formula in mathematical statistics. It is applied to all kinds of things in life. The smaller the variance, the more stable the data set, and the larger the variance, the more unstable the data set.

The concept and calculation formula of variance, for example, the scores of two people in five exams are as follows: x: 50, 100, 100, 60, 50, and the average e (x) = 72; Y: 73, 70, 75, 72, 70 Average E(Y)=72. The average score is the same, but x is unstable and deviates greatly from the average. Variance describes the deviation between random variables and mathematical expectations. A single deviation is the average of the square deviation, that is, the variance without the influence of symbols, which is recorded as E(X): the direct calculation formula separates the discrete type from the continuous type. A calculation formula is also derived: "variance is equal to the average of the sum of squares of deviations of each data and its arithmetic average". Among them, they are discrete and continuous calculation formulas respectively. It is called standard deviation or mean square deviation, and variance describes the degree of fluctuation.