利用组合恒等式求数学期望与方差

Solving Mathematical Expectation and Variance through Combinatorial Identities

直接从随机变量的数学期望与方差的定义出发,运用组合恒等式,给出了超几何分布和负二项分布的数学期望与方差的求解过程.该方法简洁明了,容易理解和掌握.

Directly from the definitions of mathematical expectation and variance of random variables, by using combinatorial identities, we give the solution to the mathematical expectation and variance of hyper-geometric distribution and negative binomial distribution. This method is concise, easy to understand and use.