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-“利润”Profit
Different definitions不同的定义
We said earlier that profit was the money a firm has left over after its costs are taken away from its revenues. So total profit = total revenue - total cost (TR − TC).
我们之前说过，利润是公司从收入中扣除成本后剩下的钱。所以总利润 = 总收入 - 总成本 (TR - TC)。
It is also worth noting that Profit per unit can be calculated by subtracting average cost from average revenue (AR − AC).
This leaves average profit, which is profit per unit. Of course, once you have average profit, you can work out total profit; simply multiply by the number of units sold (or output, Q).
还值得注意的是，单位利润可以通过从平均收入中减去平均成本来计算（AR - AC）。这留下了平均利润，即每单位的利润。当然，一旦你有了平均利润，你就可以算出总利润；只需乘以售出的单位数量（或产量，Q）。
At this point it is probably worth explaining the difference between normal profit and super-normal profit (or abnormal profit).
在这一点上，可能值得解释正常利润和超正常利润（或异常利润）之间的区别。
Normal profit occurs at the level of output where total revenue = total cost (TR = TC). At this point, average revenue = average cost as well. In other words, the firm is at break-even point.
正常利润出现在总收入 = 总成本 (TR = TC) 的产出水平上。此时，平均收入 = 平均成本也是如此。换句话说，公司处于盈亏平衡点。
Of course, included in the total costs are the firm's wage bill and the 'wage' of the boss, so breaking even is not the end of the world.
Some textbooks refer to normal profits as the firm's opportunity cost, because if the firm's profit drops below this level in the long run, the resources (or factors of production) would transfer to a different industry (a different use) where they can earn at least normal profit.
当然，总成本中包括公司的工资单和老板的“工资”，所以收支平衡并不是世界末日。一些教科书将正常利润称为企业的机会成本，因为如果企业的利润长期低于这个水平，资源（或生产要素）将转移到不同的行业（不同的用途），在那里他们可以赚取最小的正常利润。
Super normal profit is any profit over and above normal profit. If you asked the 'man-in-the-pub', this is the definition he would give; where total revenue is greater than total cost (or TR > TC).
超正常利润是超出正常利润的任何利润。如果你问“酒吧里的人”，这就是他给出的定义；其中总收入大于总成本（或 TR > TC）。
利润最大化
This is a very important concept. The assumption of maximisation is used in all models of market structure (at A level, anyway).
To be fair, it is quite a reasonable assumption, although in the real world firms (or rather the managers who run the firms) can have different objectives, like sales maximisation (the manager's salary might be linked to sales), for example.
这是一个非常重要的概念。市场结构的所有模型（无论如何都在 A 级）都使用了最大化假设。公平地说，这是一个相当合理的假设，尽管在现实世界中，公司（或者更确切地说是经营公司的经理）可能有不同的目标，例如销售最大化（经理的薪水可能与销售额挂钩）。
One way that a firm might work out the level of output where profits are maximised is to find the level of output where the difference between total revenue and total cost is largest.
公司计算利润最大化的产出水平的一种方法是找到总收入和总成本之间的差异最大的产出水平。
In the diagram above, you see the total revenue curve and the total cost curve on the same axes.
As one would expect, given the fixed costs, a firm actually makes a loss at low levels of output. It only starts to make a profit after the level of output rises above Q1 (which is a break-even level of output).
The distance between the total revenue curve and the total cost curve is greatest at Qmax, so this is the profit maximising level of output.
Profits fall after this point, reaching another break-even level of output at Q2, after which point the firm is again making a loss, given the acceleration of marginal costs due to diminishing marginal returns.
在上图中，您可以在同一轴上看到总收入曲线和总成本曲线。正如人们所预料的那样，考虑到固定成本，一家公司实际上会在低产量水平下亏损。只有在产出水平超过 Q 1（这是一个盈亏平衡的产出水平）之后，它才开始盈利。总收益曲线和总成本曲线之间的距离在 Q max处最大，因此这是利润最大化的产出水平。在这一点之后利润下降，在第二季度达到另一个盈亏平衡的产出水平，此后公司再次亏损，因为边际收益递减导致边际成本加速。
This method of working out the profit maximising level of output makes sense, but relies on trial and error rather a lot.
The following method is more precise. Although probably no easier to use for a businessman (especially one who does the books himself), it is vital for the A level economist as it is used to assess the profit maximising level of output in all diagrams associated with market structure.
这种计算利润最大化输出水平的方法是有意义的，但很大程度上依赖于反复试验。下面的方法更精确。尽管对于商人（尤其是自己做账的人）来说可能并不容易使用，但对于 A 级经济学家来说至关重要，因为它用于评估与市场结构相关的所有图表中的利润最大化产出水平。
In the diagram above you can see the marginal cost curve (MC) and the Marginal revenue curve (MR).
Profit maximisation occurs at the level of output where MC = MR.
This is one of the most important little formulas to remember in A level economics. So why are profits maximised when this occurs?
在上图中，您可以看到边际成本曲线 (MC) 和边际收益曲线 (MR)。利润最大化发生在MC = MR的产出水平上。这是 A-level 经济学中要记住的最重要的小公式之一。那么为什么在这种情况下利润最大化呢？
Let's think of a level of output below Qmax. At Q3, marginal revenue is greater then marginal cost. This means that the extra revenue gained through the sale of that unit is greater than the cost of making it.
The firm is making a profit on that unit. But this does not mean that the firm is maximising total profit. What happens if the firm makes one more unit, taking it to the level of output Q4?
Marginal revenue is still greater than marginal cost, so the firm again makes profit on that unit.
This will be true for every unit that they produce up to Qmax, so they should make all of these units.
让我们考虑低于 Q max的输出水平。在 Q 3，边际收益大于边际成本。这意味着通过出售该单位获得的额外收入大于制造成本。该公司正在从该单位获利。但这并不意味着公司正在最大化总利润。如果企业再生产一个单位，将产量提高到 Q 4的水平，会发生什么？边际收入仍然大于边际成本，因此公司再次从该单位获利。这对于他们生产的每一个单位都是如此，最高可达 Q max，所以他们应该制造所有这些单位。
At Q5, marginal revenue is less than marginal cost. The firm is making a loss on that unit. This is true of all units made after Qmax.
This does not necessarily mean that the firm is making a loss overall (what about all the profit made up to Qmax?), but it does mean that overall profit will be maximised at Qmax.
Even if the firm makes just one extra unit, where marginal cost is only a little bit bigger than marginal revenue, the overall profit will fall, however small.
在 Q 5，边际收益小于边际成本。该公司在该部门亏损。这适用于 Q max之后制造的所有单位。这并不一定意味着公司总体上正在亏损（Q max之前的所有利润呢？），但它确实意味着总体利润将在 Q max处最大化。即使公司只多生产一个单位，边际成本只比边际收入大一点，总利润也会下降，不管多小。
The diagram below might help you to understand.下图或许能帮助你理解。
Q1 and Q2 are the break-even levels of output. Notice that these are the levels of output where profit = 0 in the top diagram and TR = TC in the middle diagram.
Qmax is the profit maximising level of output. Notice that this is the level of output where the profit curve is at its highest in the top diagram, the gap between TR and TC is greatest in the middle diagram and MC = MR in the bottom diagram.
It is important to understand that, while profits are no longer maximised if production rises above Qmax, total profit is still positive, even though it is falling.
Just because MC is greater than MR for each unit produced after Qmax, so losses are made on each unit, it does not mean that the firm is making a loss overall.
This only happens when the firm's output rises above Q2.
Q 1和 Q 2是产出的收支平衡水平。请注意，这些是顶部图表中的利润 = 0 和中间图表中的 TR = TC 的输出水平。
Q max是利润最大化的产出水平。
请注意，这是利润曲线在上图中最高的产出水平，TR 和 TC 之间的差距在中图中最大，而 MC = MR 在下图中。
重要的是要理解，虽然如果产量超过 Q max利润不再最大化，但总利润仍然是正的，即使它正在下降。
仅仅因为在 Q max之后生产的每个单位的 MC 大于 MR，所以每个单位都亏损，并不意味着公司整体亏损。只有当公司的产出高于 Q 2时才会发生这种情况。
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~
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