This paper provides a simple and intuitive explanation of the demand and supply model based on the cost-benefit rule. This rule states that an action (e.g. to buy or to sell) should be undertaken only if its benefits are greater than its costs. The approach is not novel, but standard introductory textbooks only use it to explain few isolated aspects of the demand and supply model. In this paper the demand and the supply are both fully derived by simply sorting and counting the transactions that pass the cost-benefit rule for buyers and sellers. The emphasis on this rule has two main advantages. First, it makes the model more relatable, as it is more easily applied to everyday concepts and decisions students are familiar with. Second, it provides new students of economics with a clear explanation of how, in general, the discipline of economics approaches the analysis of decisions and behavior.

本文根据成本效益规则对需求和供应模型进行了简单直观的解释。该规则规定，只有在其收益大于成本的情况下，才应采取行动（例如，购买或出售）。这种方法不是新颖的，但是标准的入门级教科书仅使用它来解释需求和供应模型的几个孤立方面。在本文中，需求和供应都可以通过简单地对通过了买卖双方成本收益规则的交易进行分类和计数而完全得出。强调此规则有两个主要优点。首先，它使模型更相关，因为它更容易应用于学生熟悉的日常概念和决策。其次，它为经济学的新学员提供了一个总体上如何清晰地解释的解释，