Bertrand rule

例句：

1. 1. The Bertrand rule states that the cost of a good is equal to its price divided by its price per unit.
   伯特兰规则指出，一件商品的成本等于其价格除以单位价格。
2. 2.This is an example of the Bertrand rule in action.
   这是一个伯特兰规则应用的例子。
3. 3. According to the Bertrand rule, if two goods are identical in quality but different in price, consumers will choose the cheaper one.
   根据伯特兰规则，如果两种商品在质量上相同但价格不同，消费者会选择价格较低的那一种。