假设单个汽车生产商的固定成本是50亿美元，而每辆车的可变成本是17000美元。厂商越多，竞争越激烈

，价格就下降。具休说，n为市场上厂商的数量。设美国和欧洲市场上分别有3亿和5.33亿人口。

a.在没有对外贸易时，美国和欧洲汽车市场上均衡的厂商数量是多少？

b.在没有对外贸易时，美国和欧洲汽车市场上均衡的价格是多少？

c.现在假设美欧之间进行自由贸易，美国市场上除了原有的3亿人口外，将增加5.33亿人口。在美国和欧洲汽车市场上将有多少汽车厂商？汽车新的均衡价格是多少？

d.美国市场上汽车的价格在b和c中为何不同？自由贸易改善了消费者的福利吗？是怎样改善的？

Suppose that fixed costs for a firm in the automobile industry (start- up costs of factories， capital equipment， and so on) are $5 billion and that variable costs are equal to $17，000 per finished automobile. Because more firms increase competition in the market， the market price falls as more firms enter an automobile market， or specifically， where n represents the number of firms in a market. Assume that the initial size of the U.S. and the European automobile markets are 300 million and 533 million people， respectively.

a.Calculate the equilibrium number of firms in the U.S. and European automobile markets without trade.

b.What is the equilibrium price of automobiles in the United States and Europe if the automobile industry is closed to foreign trade？

c.Now suppose that the United States decides on free trade in automobiles with Europe. The trade agreement with the Europeans adds 533 million consumers to the automobile market， in addition to the 300 million in the United States. How many automobile firms will there be in the United States and in Europe combined？ What will be the new equilibrium price of automobiles？

d.Why are prices in the United States different in (c) than in (b) ？ Are consumers better off with free trade？ In what ways？