为什么正常利润包括在总成本中(正常利润包含在成本中)

A-level economics revision guides and question banks covering labour markets, supply and demand, market structure and all core economics a-level topics.

以下内容我们会持续更新：

今天带给大家Alevel经济笔记是：

成本和收入-Revenues and their Curve

First, we need to define revenue. The revenue of a firm constitutes the receipts of money from the sale of goods and services over a given time period.

Some textbooks also refer to the revenue of a firm as its turnover.

首先，我们需要定义收入。公司的收入构成了在给定时间段内销售商品和服务的收入。一些教科书还将公司的收入称为营业额。

Many students confuse revenue with profit (see the next Learn-It).

It is easy to mistakenly talk about revenue as the amount of money that the firm 'makes'.

The amount of money that a firm 'makes' is the profit; it is the amount of money left after costs are taken away from revenue.

许多学生将收入与利润混为一谈（参见下一个 Learn-It）。很容易将收入误认为是公司“赚到”的钱。公司“赚”的钱就是利润；它是从收入中扣除成本后剩下的金额。

总收入、边际收入和平均收入

Now we need to look at specifics: total, average and marginal revenue.

Total revenue (TR). This is the total receipts of money received by a firm from the sale of its good or service in a given time period.

It can be calculated by multiplying the quantity sold by the price at which the goods were sold, or TR = P × Q.

总收入 (TR)。这是公司在给定时间段内从销售其商品或服务中收到的总收入。它可以通过将售出的数量乘以商品的售出价格来计算，即 TR = P × Q。

Average revenue (AR). This is the amount of money received, on average, for each good sold. If you think about it, this is effectively the price.

平均收入 (AR)。这是平均每售出一件商品所收到的金额。如果您考虑一下，这实际上就是价格。

We know that TR = P × Q, so we can substitute this into the equation above:

我们知道 TR = P × Q，所以我们可以将其代入上面的等式：

Marginal revenue (MR). Marginal cost is the cost of producing one more unit of output. Marginal revenue is the revenue received from selling one more unit of output.

It is the extra revenue at the margin (i.e. by selling the marginal unit of output).

边际收入（MR）。边际成本是多生产一单位产品的成本。边际收入是从多销售一单位产品中获得的收入。它是边际的额外收入（即通过出售边际单位产出）。

As with the Learn-It on costs, it is worth looking at these relationships in more detail. Look at the table below.

Q, which was output in the cost table, now represents sales for our laser printer firm. All revenue figures are in pounds.

与关于成本的 Learn-It 一样，值得更详细地研究这些关系。请看下表。Q 是成本表中的输出，现在代表我们激光打印机公司的销售额。所有收入数字均以英镑为单位。

The first column shows the progressive units of output sold.

第一列显示了销售产出的累进单位。

The second column shows average revenue.

Notice that this figure falls as the quantity sold (or demanded) rises. Remember also that AR = price. So in essence as the price falls, demand rises.

As you will see when we draw the diagrams in the next sub-section, the AR curve is the demand curve!

第二列显示平均收入。请注意，这个数字随着销售（或需求）数量的增加而下降。还要记住 AR = 价格。所以本质上，随着价格下跌，需求上升。正如您将在我们在下一小节中绘制图表时看到的那样，AR 曲线就是需求曲线！

The third column shows total revenue. As we said earlier, TR = P × Q.

So the figures in this column were calculated by multiplying the number in the first column (Q) by the corresponding number in the second column (P). So, TR = Q × AR.

第三列显示总收入。正如我们之前所说，TR = P × Q。所以这一列中的数字是通过将第一列（Q）中的数字乘以第二列（P）中的相应数字来计算的。因此，TR = Q × AR。

The final column shows marginal revenue.

Using the same method as we did for marginal cost and marginal product, the marginal revenue for, say, the seventh good sold is the difference between the total revenue received from selling 7 units and the total revenue received from selling 6 units.

Algebraically, MR7 = TR7 − TR6 = 1260 − 1200 = 60.

最后一列显示边际收入。使用与边际成本和边际产品相同的方法，例如，销售第七种商品的边际收入是销售 7 件商品的总收入与出售 6 件商品的总收入之间的差额。代数上，MR 7 = TR 7 - TR 6 = 1260 - 1200 = 60。

Now try and work out the answers to the table below. Click on the relevant sections in the table to reveal the answers.

现在试着找出下表的答案。单击表中的相关部分以显示答案。

总收入、边际收入和平均收入曲线

In the last section, an important fact was revealed. The AR curve is, in fact, the firm's demand curve.

Demand curves tell you how much of a good is demanded at any given price. But they can also tell you the price for a given level of demand.

So if the AR curve is the price curve, then it must also be the demand curve.

在上一节中，揭示了一个重要事实。AR 曲线实际上是企业的需求曲线。需求曲线告诉您在任何给定价格下需要多少商品。但他们也可以告诉你给定需求水平的价格。因此，如果 AR 曲线是价格曲线，那么它也一定是需求曲线。

In the topic called 'Market structure', you will see that firms in most market structures have 'normal' downward sloping demand curves. In the unique market structure of perfect competition, firms have a horizontal, or perfectly elastic demand curve.

There are two sets of diagrams below. The first set looks at the case where the firm in question has a downward sloping demand (AR) curve. The second set looks at the more unusual case where the demand (AR) curve is perfectly elastic.

在名为“市场结构”的主题中，您将看到大多数市场结构中的公司都有“正常的”向下倾斜的需求曲线。在完全竞争的独特市场结构中，企业具有水平的或完全弹性的需求曲线。下面有两组图表。第一组着眼于所讨论的公司具有向下倾斜的需求 (AR) 曲线的情况。第二组着眼于需求（AR）曲线完全弹性的更不寻常的情况。

当 AR 曲线是“正常”向下倾斜的需求曲线时

The diagrams are just sketches, this is totally acceptable with examiners. They are more bothered about the quality of your written analysis that goes with the diagram (although the diagram itself is always very important)!

图表只是草图，考官完全可以接受。他们更关心图表附带的书面分析的质量（尽管图表本身总是非常重要）！

In the top diagram, we have the downward sloping demand curve (AR) and a marginal revenue curve that is falling twice as fast.

If you look at the figures in the tables above, this is what you should expect. Do you remember the relationship between all marginals and averages outlined in the 'Costs and their curves? Learn-It?

If the marginal is below the average (regardless of whether the marginal is rising or falling), then the average will fall. This is also true with the revenue curves.

在上图中，我们有向下倾斜的需求曲线 (AR) 和一条以两倍速度下降的边际收益曲线。如果您查看上表中的数字，这就是您所期望的。您还记得“成本及其曲线”中概述的所有边际和平均值之间的关系吗？学习它？如果边际低于平均值（不管边际是上升还是下降），那么平均值就会下降。收入曲线也是如此。

I have deliberately put the total revenue curve underneath the other two curves. Notice that the TR curve is at a maximum when the MR curve cuts the x-axis (i.e. when MR = 0). This makes sense.

我故意将总收入曲线放在其他两条曲线的下方。请注意，当 MR 曲线穿过 x 轴时（即 MR = 0 时），TR 曲线处于最大值。这是有道理的。

As MR falls, the extra revenue gained from the sale of the last unit is falling with every unit sold, but it is still positive. This is why the TR curve keeps rising, albeit at a declining rate.

随着 MR 的下降，从最后一个单位的销售中获得的额外收入随着每售出一个单位而下降，但仍然是正数。这就是为什么 TR 曲线不断上升，尽管速度下降的原因。

When MR hits the x-axis, the last unit sold added no revenue to the total, so the TR curve remains unchanged (it is momentarily flat).

当 MR 到达 x 轴时，最后售出的单位没有增加总收入，因此 TR 曲线保持不变（暂时平坦）。

As successive marginal revenues are negative, the total does finally fall.

由于连续的边际收入为负，总收入最终确实下降。

当 AR 曲线是平坦的需求曲线时

Why is the firm's demand curve (AR curve) the same as its marginal revenue curve? Again, it's down to the relationship between averages and marginals.

Do you remember the example with the money you and your friends have on you as you wait at the bus stop?

If, on average, all nine of you have £20 each, and a tenth friend turns up with £20, then the average for the ten of you is still £20 each.

为什么企业的需求曲线（AR 曲线）与其边际收益曲线相同？同样，这取决于平均值和边际之间的关系。你还记得你和你的朋友在公共汽车站等车时身上带的钱的例子吗？如果平均而言，你们九个人每人有 20 英镑，而第十个朋友带着 20 英镑出现，那么你们十个人的平均数仍然是每人 20 英镑。

In the diagram above, the perfectly elastic AR curve is flat, so the value for average revenue stays the same. If the average is always the same, then the marginal must be constant and the same value as the average. So the two curves are the same.

在上图中，完全弹性的 AR 曲线是平坦的，因此平均收入的值保持不变。如果平均值始终相同，则边际必须是常数并且与平均值相同。所以两条曲线是一样的。

As the marginal revenue is constant, the extra revenue added to the grand total every time a unit is sold is the same for every unit. Hence, total revenue is continually rising and at a constant rate.

由于边际收入是恒定的，因此每次售出一个单位时添加到总计中的额外收入对于每个单位都是相同的。因此，总收入以恒定的速度不断增长。

今天的Alevel经济笔记就更新到这里，如果大家对Alevel经济学感兴趣可以关注我们，

之前更新：

1、Alevel经济学习笔记：总需求和总供给篇-The Circular Flow of Income

2、Alevel经济学习笔记：总需求和总供给篇-The '45 Degree' Diagram

3、Alevel经济学习笔记：总需求和总供给篇-Aggregate Demand

后续我们还会更新我以下版块的内容~