问题 问答题

完全竞争市场上,目前存在三家生产相同产品的企业,q表示各企业的产量,各企业生产成本函数如下。企业1的短期生产函数为C1(q)=18+2q2+20q,企业2的短期生产函数为C2(q)=25+q2,企业3的短期生产成本函数为C3(q)=12+3q2+5q。试求:

(1)该产品的市场价格处于何种范围时,短期内三家企业的产量都为正(需要说明理由)

(2)短期市场供给曲线与长期市场供给曲线。

答案

参考答案:

此类题首先要理清MC、AC、AVC,理清了它们,分析起来就方便多了。

(1)产量为正的要求是MC≥AVC,我们可以根据MC=AVC来分析:

由C1=18+2q2+20q可知:MC1=-4q+20,AVC1=2q+20

由MC1=AVC1得:4q+20=2q+20gmin=0p1=AVC1=20

由C2=25+q2可知:MC2=2q,AVC2=q

由MC2=AVC2得:2q=q>qmin=0p2=AVC2=0

由C3+12+3q2+5q可知:MC3=6q+5,AVC3=3q+5

由MC3=AVC3得:6g+5=3g+5qmin=0p3=AVC3=5

只有市场价格p≥max(p1,P2,P3)=20时,才可能三家企业都选择短期生产,即产量都为正。

(2)如果0≤市场价格p<5,市场上只有企业2生产,此时供给曲线Q=q2

如果5≤市场价格p<20,企业2与企业3都会生产,此时供给曲线Q=q2+q3

如果市场价格p≥20,三家企业都会生产,此时供给曲线Q=q1+q2+q3

所以,短期市场供给曲线为:

容易看出该完全竞争行业为成本递增行业,长期供给曲线理论上为向右上倾斜的曲线。

由于完全竞争行业不存在超额利润,长期成本高的厂商如果不能使MC=P则会退出,剩下的是满足MC=P的厂商,或者由于厂商增多引起行业MC上升,连MC最低的厂商也不能满足MC=P。考虑这两种情况的长期供给曲线为:

Q=0,或Q=,p≥0。

单项选择题

With one eye turned towards keeping its own economy on track and the other trained fearfully on the impact of the global economic downturn, China has announced a four trillion yuan ($ 586 billion) stimulus package, the largest in the country’s history.

Unveiled by China’s State Council on the evening of Sunday November 9th, the two-year spending initiative will inject funds into ten sectors, including health care, education, low- income housing, environmental protection, schemes to promote technological innovation, and transport and other infrastructure projects. The government also says that some of the spending will be directed to reconstruction efforts in areas battered by natural disasters, such as Sichuan province which was devastated by a massive earthquake in May.

"Over the past two months, the global financial crisis has been intensifying daily," the State Council said in a statement. "In expanding investment, we must be fast and heavy- handed. " News of the stimulus package has been welcomed by global investors. Asian and European stock markets rose on Monday, with American markets also climbing. China’s decisive move is likely to please foreign governments which are now grappling with the global downturn. It comes a few days before the Chinese president is scheduled to attend a global economic summit in Washington D. C. , and a day after Hu Jintao had spoken by phone to the American president-elect, Barack Obama, about the global economic crisis and other issues.

China’s government has so far provided few details of when the money will be spent or how it will be divided. Officials do say that fourth quarter investment for this year will total 400 billion yuan, including 20 billion yuan brought forward from next year’s central government budget. If fully realised, the two-year spending spree would amount to about 16% of China’s annual gross domestic product.

The newly announced measures also include a loosening of credit policies and tax cuts. The plan calls for reforms in the country’s value-added tax regime that would save industry 120 billion yuan, according to an estimate by the government. Credit ceilings for commercial banks are to be abolished in the hope of channelling more capital to small enterprises, rural areas and unspecified "priority projects".

The government is concerned about the potential for frivolous or speculative investments, so the State Council also decreed at its meeting on Sunday that credit expansion must be "rational" and should "target spheres that would promote and consolidate the expansion of consumer credit". Finding ways to get Chinese consumers spending should be a priority. Unleashing domestic demand has been a longstanding goal of Chinese policymakers, but Chinese consumers-with few of their health-care or retirement needs reliably met either by employers or the state-often prefer to save.

China has sustained double-digit economic growth rates over the past five years but the economy has been slowing, considerably in some sectors. The economy logged a growth rate of 11.9% last year, but many forecasters believe that it will dip below 10% this year, with fourth-quarter growth down to 6% or even lower.

Growth rates in that range may be the envy of recession-battered economies, but mark signs of trouble for China. It is an article of faith among many economists-and a view publicly stated earlier this year by the Chinese Prime Minister, Wen Jiabao-that China needs a growth rate of at least 7% to avoid massive unemployment. The country has been hurt in recent months by softening export markets, depressed domestic property values and stock markets, and declining consumer and investor confidence.

According to the text, which of the following is NOT the phenomenon caused by the economic downturn()

A. The export markets are being softened

B. Domestic property value is being depressed

C. Number of people that go vacation abroad sharply reduced

D. Consumer and investor confidence declined daily

单项选择题