These sum problems are all difficult for using elementary method and analysis method, but we can easily solve these sum problems by using the probability method.
而这几个公式的求和问题不论是用初等方法或分析方法都是比较困难的，但用概率的方法却比较容易解决。
2
At last, the mathematical model has also been made on the coefficient of probability important degree of the elementary events.
最后，还建立了基本事件概率重要度系数的数学模型。
3
The formula of total probability, conditional probability and bayes formula are elementary formulas of probability theory.