请问曼昆书里边的这道题究竟怎么理解，能讲详细一点吗？

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5．你管理的公司在开发一种新产品过程中已经投资500 万美元，但开发工作还远远没
有完成。在最近的一次会议上，你的销售人员报告说，竞争性产品的进入使你们新产品的预
期销售额减少为300 万美元。如果完成这项开发还要花费100 万美元，你还应该继续进行这
项开发吗?为了完成这项开发你应该最多花费多少?

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关键词：销售人员 新产品 竞争性 销售额 曼昆

应该继续开发，最多花费200万美元。
因为500万是沉没成本。

这道题里怎么理解边际成本和边际利益，有没有详细的解释啊

应该继续开发，最多花费是300万美元吧。

没人能解释清楚点？

我同意2楼得哥们的解答，应该继续开发，因为刚开始开发时说明预期的销售额因该 是大于等于500，由于竞争产品的进入是你的预期销售额减少了300，但前期的投入已属沉默成本，后期的成本是100，而带来的预期收入至少是200，MR>MC按照边际法则，你是应该继续投入的。小弟愚见了。望楼主明鉴！

我觉得那个最多的花费应该是你的预期销售额减去300的值但是题中并没说预期销售额是多少，只要MR=MC时就该是那个最大花费的值了

这道题应该是前面高手说的关于sunk costs的。sunk costs在做决定的时候是不用考虑的。计算npv就知道最多投资多少了。cost和产出量的关系似乎不明确，所以很难计算marginal cost. 同样也不好算marginal revenue.

当然这是传统经济学的论点。维基百科提到: ``In economics and business decision-making, sunk costs are retrospective (past) costs that have already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken. Both retrospective and prospective costs may be either fixed (that is, they are not dependent on the volume of economic activity, however measured) or variable (dependent on volume).

In traditional microeconomic theory, only prospective (future) costs are relevant to an investment decision. Traditional economics proposes that an economic actor not let sunk costs influence one's decisions, because doing so would not be rationally assessing a decision exclusively on its own merits. The decision-maker may make rational decisions according to their own incentives; these incentives may dictate different decisions than would be dictated by efficiency or profitability, and this is considered an incentive problem and distinct from a sunk cost problem.

Evidence from behavioral economics suggests this theory fails to predict real-world behavior. Sunk costs greatly affect actors' decisions, because many humans are loss-averse and thus normally act irrationally when making economic decisions.''

行为经济学认为sunk costs是有影响的。