在 SAIS AP 微观经济学课程中，学生目前正在学习四种主要市场类型之一的完全竞争，并探索它在日常业务运营中的运作方式。我希望您会喜欢我们的学生如何简要分析各种课程概念，并通过经济模型和现实生活应用之间的个性化示例建立独特的联系。

At SAIS AP Microeconomics class, students are currently learning about one of four main market types called perfect competition, and exploring how it works in daily business operations. I hope you will enjoy, how our students briefly analyzed various lesson concepts and made unique connections with personalized examples between economic models and real-life applications. 

规模经济：规模经济的基本概念是，当企业规模越来越大时，代表长期平均总成本的LRATC可能先下降后上升，最后可能表现为U-图形中的形状。这听起来很复杂，但如果我们有一个很好的例子，它可能很容易理解。让我们谈谈记录。假设有一个乐队需要在这里录制他们的新专辑，那么效率就不会高，因为他或她无法处理所有事情。因此，团队决定聘请一位能够处理麦克风和其他制作材料的制作人。录制完成后，他们需要经理帮助他们发行专辑，并使CD能够合法地出现在商店里。他们雇了一个，使工作更有效率。他们靠专辑赚钱，他们决定发行一些黑胶唱片，显然这不经济，但它使规模更大。随着他们生产更多，他们的平均成本暂时没有变化。乐队在国外走红，澳洲很多人也想买他们的专辑，所以他们提供国外快递，LRATC因为规模大而增加。

Economics of scale: The basic concept of the economics of scale is that when the business get bigger and bigger, the LRATC, which stand for long run average total cost, may fall at first then goes up and finally It might be showed in U-shape in graphs. It sounds pretty complex, but it could be easy to understand if we have a nice example.  Let’s talk a little bit about record.  Assumes that there is a band who need record their new album here, it cannot be efficient because he or she cannot deal with everything.  So the team decide to hire a producer who is able to deal with microphone and other producing stuff. After recording, they need a manager to help them releasing the album and make the CD can appear in the shop legally. They hired one and make the working more efficient.  They got money by the album, and they decide to release some vinyl records, obviously it’s not that economics, but it make the scale bigger. As they produce more, their average cost have no change for a while. The band get popular abroad, lots of people in Australia want to buy their album as well, so they offer abroad express, the LRATC increase because the big scale. 

——Jason Shaw, G9

我们了解了生产成本和完全竞争。我将谈论利润的类型。现在让我们理清概念。

首先，总收入是总价格，公式是价格 x 数量。例如，如果您生产 2 个杯子蛋糕，每个杯子蛋糕的价格为 3。总收入为 3x2=6

总利润公式为总收入-总成本。例如，如果生产 2 个杯子蛋糕，成本为 2 美元。现在利润是 6 – 2 = 4

并且有两种利润。还有会计利润和经济利润。

会计利润公式是总收入 - 会计成本（仅明确）

经济利润公式为总收入-经济成本（显性+隐性）

显性是你看得见的成本，隐性是你看不到的成本。比如日常生活中你放弃工作看电影，电影票的成本是你的显性成本，你可以从工作中赚取的是你的隐性成本。

We learned the production costs and perfect competition. I will talk about the types of profit. Now let’s clear the concept. 

First , the total revenue is total price the formula is price x Quantity. For example if you produce 2 cup cake each cup cake price is 3. Your total revenue is 3x2=6 

The total profit formula is total revenue – total cost . For example  if you produce 2 cup cake and your cost 2 dollar . Now your profit is 6 – 2 = 4 

And there are two types of profit . There are accountant and economic profit . 

The accounting profit formula is  total revenue – accounting costs (explicit only) 

Economic profit formula is total revenue – economic costs(explicit+ Implicit) 

The explicit is the costs that you can see ，implicit is the cost that you can’t see.Example for daily life is you give up the work to watch a movie, the costs of movie tickets is your explicit cost, and the money that you can earn from the work is your implicit cost.

——Lucy Yang, G9

在完全竞争市场中，边际成本=价格（MC=P），其中所有供应商都是价格接受者。完全竞争的最高效率是“静止”，在技术层面。

首先，市场上有大量的供应商。没有供应商能够影响市场。第二，一致的产品，所有供应商提供相同的产品。第三，完善的信息，所有供应商都知道其他公司的价格设定。第四，同样的准入，所有供应商都有权使用所有产品技术。五、自由进出，所有供应商均可自由进出市场

如果一家甜甜圈店A在这个市场上是盈利的，当有新的竞争者进入市场时，甜甜圈公司A不再盈利，所以一些甜甜圈公司选择退出市场。在长期均衡的完美市场中，利润率是相同的。此外，公司进入和退出市场的时间是相同的。

In a perfectly competitive market, marginal cost = price (MC=P) in which all suppliers are price takers. The highest efficiency in perfect competition is "stationary", at the technical level. 

First, there are a large number of suppliers in the market. No suppliers are able to influence the market. Second, consistent products, all suppliers offer the same products. Third, perfect information, all suppliers know the price setting of other companies. Forth, same access, all suppliers have the right to use all product technology. Fifth, free entry and exit, all suppliers are free to enter and leave the market 

If a donut store A is profitable in this market, when a new competitor enters the market, donut company A is no longer profitable, so some donut companies choose to leave the market. In a perfect market in long term equilibrium, the ratio of profits is the same. Also the time of entering and leaving the market is the same for companies. 

——King  Yao, G10

需求价格弹性：让我们考虑一个热门风景区的冰淇淋店。夏季，由于游客在炎热的天气更愿意购买冰淇淋，冰淇淋店的销售额大幅增加。

然而，商店也注意到，当他们提高冰淇淋的价格时，他们的销量会下降。因此，如果他们想增加收入，他们可能需要在提高价格和维持客户需求之间找到平衡点。

如果他们提高价格太多，他们可能会将客户流失给以更低价格提供类似产品的竞争对手。另一方面，如果公司降价太多，他们可能无法赚取足够的利润来维持业务。因此，了解需求的价格弹性对于企业做出定价决策和保持市场竞争力至关重要。

Price Elasticity of Demand: Let's consider an ice cream store in a popular scenic area. During the summer, the ice cream parlor's sales increase significantly as tourists are more willing to buy ice cream in the hot weather. 

However, the store also notices that when they raise the price of ice cream, their sales will decrease. So, if they want to increase revenue, they may need to find a balance between raising prices and maintaining customer demand. 

If they raise prices too much, they may lose customers to competitors who offer similar products at lower prices. On the other hand, if companies lower their prices too much, they may not earn enough profit to maintain their business. Therefore, understanding the price elasticity of demand is critical for firms to make pricing decisions and remain competitive in the marketplace. 

——Karlie Liu G10

在我们的 AP 微观经济课上，我们学到了许多不同的东西，然后我们可以将它们应用到现实生活中，最近我们完成了第三单元。这个单元是关于生产成本和完全竞争的。生产成本是您为了生产产品而必须使用或放弃的一切。完全竞争是指买卖双方数量众多，商品的市场价格不受个别买卖双方的控制。

In our AP Micro-economic class we have learned about many different things that we are then able to apply to real life, most recently we finished the third unit. This unit was all about the costs of production, and perfect competition. Costs of production are everything that you have to use, or give up, in order to produce a product. Perfect competition is when there are a multitude of buyers and sellers, and the market price of a good, is beyond the control of individual buyers and sellers. 

——Simon Abbott, G11

完全竞争：如果一家公司在完全竞争中销售糖果，并且如果需求增加，价格就会上涨，公司就会获利。那么会有更多的公司进入这个市场。然后价格会下降。但如果很多公司卖糖果，但只有一点点人买，那么很多公司就会退出这个市场。

收益递减：如果你有一家餐馆，你需要聘请厨师。厨房不能改变，但你可以赚到很多厨师。起初，你有一个厨师，但效率很低。随着你聘请的厨师人数越多，效率就越高。但如果你雇用太多厨师，他们就没有足够的工作要做。然后效率开始下降。

Perfect competition:  if one company is selling the candy in perfectly competitive, and if the demand increase, the price will increase the company will earn profit. Then there will be more company enter this market. Then the price will decrease. But if many company sell candy but just a little bit people buy it, then many company will retreat from this market. 

Diminishing return: if you have a restaurant and you need to hire chef. The kichen can’t change but you can earn many chefs. At first, you have one chef but the efficient is low. As the number the chef you hire more, the efficient is higher and higher. But if you hire too much chefs, they don’t have enough work to do. Then the efficient begin to decrease.  

——William Feng, G9