说明：  一. 随机现象的模拟 例： 超市出口有若干个收款台，两项服务：收款、装袋。顾客的到达的时间间隔是随机的； 因顾客购买的货物量不同，所以服务时间的长短也是随机的。 可以利用计算机产生服从一定的规律（概率分布）的(伪)随机数，用随机数确定时间间隔和服 务时间
(1. Random phenomena simulation cases: There are a number of export supermarket cashier, the two services: collection, bagging. Customer' s arrival time interval is random due to the amount of freight customers to buy different, length of service is also random. Can make use of computer-generated subject to certain rules (probability distribution) of the (pseudo) random numbers, using a random number to determine the time interval and service time)