1, let x be a random variable and c be a constant, then ECX is equal to c times EX.

2. Let x and y be any two random variables, then there is EX plus y equal to EX plus EY.

3. If x and y are independent random variables, then EXY equals EX times EY. In statistics, when estimating the expected value of a variable, the common method is to measure the value of this variable repeatedly, and then use the average value of the obtained data as the estimation of the expected value of this variable. In probability distribution, expected value and variance or standard deviation are important characteristics of distribution.