请问老师，完全竞争市场中，记得讲过P=MR，不记得有讲过P=MC，而且如果P=MC的话，那MR也等于MC，那这不是利润最大化的条件吗？而题目用到的应该是breakeven的条件啊，请解答。
问题如下图：
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解释：
NO.PZ2018062003000067 问题如下 For a market of perfecompetition, the manschele is fineP = 165– 3Q (for Q ≤ 55). For eacompany in the long-run, the totcost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the margincost is given by: 1 + 10Q. whiof the following price, new competitors are most likely to enter? A.135. B.51. C.45. B is correctIn a perfectly competitive market, for eacompany in the long-run, only when MC = = P, woulthe equilibrium expectewe cthe equation:MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.thtime, P=M1 + 10Q = 51If the priis higher th51, 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 = = P，联立MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.，解得P=M1 + 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。 这道理和另一道相似的题最后求P用的方法不一致，另一道题做法P=MC=5*5+1=26，应该是这个答案。并且另一道题是因题目中P的公式是整个市场的，所以不匹配，因此不适用。。。我觉得很混乱，请辨析一下
NO.PZ2018062003000067 问题如下 For a market of perfecompetition, the manschele is fineP = 165– 3Q (for Q ≤ 55). For eacompany in the long-run, the totcost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the margincost is given by: 1 + 10Q. whiof the following price, new competitors are most likely to enter? A.135. B.51. C.45. B is correctIn a perfectly competitive market, for eacompany in the long-run, only when MC = = P, woulthe equilibrium expectewe cthe equation:MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.thtime, P=M1 + 10Q = 51If the priis higher th51, 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 = = P，联立MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.，解得P=M1 + 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。 1.请问这里为什么不能用P=MC联合立？165– 3Q =1 + 10Q.2.怎么区分啥时候是P是代表整个市场，还是代表单个厂商3.不是P=MR=MC么，为啥会出现AC?在讲义中哪里有出现呢
NO.PZ2018062003000067 问题如下 For a market of perfecompetition, the manschele is fineP = 165– 3Q (for Q ≤ 55). For eacompany in the long-run, the totcost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the margincost is given by: 1 + 10Q. whiof the following price, new competitors are most likely to enter? A.135. B.51. C.45. B is correctIn a perfectly competitive market, for eacompany in the long-run, only when MC = = P, woulthe equilibrium expectewe cthe equation:MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.thtime, P=M1 + 10Q = 51If the priis higher th51, 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 = = P，联立MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.，解得P=M1 + 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。 完全竞争市场MR=MC用已知公式推导出MR=165-6Q然后用MC=1+10Q来里联立方程，求Q=10.25，再带入p的公式算出来P=134.25
NO.PZ2018062003000067问题如下For a market of perfecompetition, the manschele is fineP = 165– 3Q (for Q ≤ 55). For eacompany in the long-run, the totcost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the margincost is given by: 1 + 10Q. whiof the following price, new competitors are most likely to enter?A.135.B.51.C.45.B is correctIn a perfectly competitive market, for eacompany in the long-run, only when MC = = P, woulthe equilibrium expectewe cthe equation:MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.thtime, P=M1 + 10Q = 51If the priis higher th51, 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 = = P，联立MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.，解得P=M1 + 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。
NO.PZ2018062003000067问题如下For a market of perfecompetition, the manschele is fineP = 165– 3Q (for Q ≤ 55). For eacompany in the long-run, the totcost is given by: 125 + Q + 5Q2, the average cost is given by: 125/Q + 1 + 5Q, the margincost is given by: 1 + 10Q. whiof the following price, new competitors are most likely to enter?A.135.B.51.C.45.B is correctIn a perfectly competitive market, for eacompany in the long-run, only when MC = = P, woulthe equilibrium expectewe cthe equation:MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.thtime, P=M1 + 10Q = 51If the priis higher th51, 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 = = P，联立MC=A1 + 10Q = 125/Q + 1 + 5Q, Q=5.，解得P=M1 + 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。 老師，我知道原理但不會求q
