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吴超 Cassie · 2022年06月25日

对解析与最终答案的匹配性存疑

  1. CFA I
  2. Economics Analysis

NO.PZ2018062003000067

问题如下：

For a market of perfect competition, the demand schedule is defined as P = 165– 3Q (for Q ≤ 55). For each company in the long-run, the total cost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the marginal cost is given by: 1 + 10Q. At which of the following price, new competitors are most likely to enter?

选项：

A.

135.

B.

51.

C.

45.

解释：

B is correct

In a perfectly competitive market, for each company in the long-run, only when MC = AC = P, would the equilibrium be expected.

we can draw the equation:

MC=AC: 1 + 10Q = 125/Q + 1 + 5Q, Q=5.

At that time, P=MC= 1 + 10Q = 51

If the price is higher than 51, new competitors will enter for economic profits .

考点：完全竞争市场

解析：在完全竞争市场中，存在条件 MC = AC = P，

联立MC=AC: 1 + 10Q = 125/Q + 1 + 5Q, Q=5.，

解得：P=MC= 1 + 10Q = 51。

注意到，之所以不用需求函数 P = 165– 3Q参与联立是因为这里给的是整个市场的需求函数，而非单个厂商的 。但是题目给定的MC,AC都是单个厂商的关系式，所以整个市场的需求函数与它们并不匹配，不能参与联立。

我的理解是厂商只有当市场中存在economic profit>0的时候新的厂商才会更愿意选择进入，当然等于0的时候也可以进入，虽然economic profit=0，但是此时可以赚取accounting profit。但是题目问的是最有可能的价格，我觉得应该是A，解析中也提到了，价格应该大于51。

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1 个答案

笛子_品职助教 · 2022年06月27日

嗨，从没放弃的小努力你好：


同学的理解是正确的。价格越高竞争者越想进入，这是没问题的。

只不过这道题，出题人的意思，是计算临界价格。CFA中类似的题目，都是要计算临界价格。

----------------------------------------------
虽然现在很辛苦，但努力过的感觉真的很好，加油！

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