同济大学经济与管理学院试卷 (B卷答案) 一、单选题：40分（每小题2分 acadb:addcd:aabbc:bbabd 二、计算题：40分（每小题20分） 1 answer )The monopolist wants to choose qu ntity to maximize its profits max=PQ-C((). =63.Q(Q.50,or=48Q.Q To determine the the change nwith the change Substitute the profit-maximizing quantity.=24.into the demand function to find price: 24=53.P.0rP=$29 Profits areequal to =TR.TC=(2924)-624)=$576. When the s 元1=Pg,-C(g)=53-21-22-5g,or 元1=53Q1-Q7-Q,Q2-5Q1 and π2=P2-C)=(53-g1-Q222-50,or2=5302-Q吃-QQ-52 3).Under the Courno mption.Firm 1 treats the output of Firm 2 tant in it maximizati 的t0ma as a constant.The change in with respect to a change in is 0-3-20-0-5=0or0=24-号 This equation is the reaction function for Firm 1,which generates the profit. maximizing level of output.given the constant output of Firm 2.Because the action function for Firm 2is
1 同济大学经济与管理学院试卷 (B 卷答案) 一、单选题：40 分（每小题 2 分） acadb;addcd;aabbc;bbabd 二、计算题：40 分（每小题 20 分） 1 answer: 1)The monopolist wants to choose quantity to maximize its profits: max = PQ - C(Q), = (53 - Q)(Q) - 5Q, or = 48Q - Q2 . To determine the profit-maximizing quantity, set the change in with respect to the change in Q equal to zero and solve for Q: d dQ Q Q 2 48 0 24 , . or Substitute the profit-maximizing quantity, Q = 24, into the demand function to find price: 24 = 53 - P, or P = $29. Profits are equal to = TR - TC = (29)(24) - (5)(24) = $576. 2). When the second firm enters, price can be written as a function of the output of two firms: P = 53 - Q1 - Q2. We may write the profit functions for the two firms: 53 5 , 1 PQ1 C Q1 Q1 Q2 Q1 Q1 or 1 11 2 53 5 Q Q QQ Q 12 1 and 53 5 , 2 PQ2 C Q2 Q1 Q2 Q2 Q2 or 2 22 2 53 5 Q Q QQ Q 12 2. 3). Under the Cournot assumption, Firm 1 treats the output of Firm 2 as a constant in its maximization of profits. Therefore, Firm 1 chooses Q1 to maximize 1 in b with Q2 being treated as a constant. The change in 1 with respect to a change in Q1 is 1 1 12 1 2 53 2 5 0 24 Q 2 QQ Q Q , . or This equation is the reaction function for Firm 1, which generates the profitmaximizing level of output, given the constant output of Firm 2. Because the problem is symmetric, the reaction function for Firm 2 is
02=24-g 2.Answer )When real GDP is $0,aggregate planned expenditure (the sum ofC++G+M)equals $4.5 trillion and unplanned inventory change (the difference between GDP and aggregate planne investment)is -S4.5 trillion.When real GDP is $2.5 trillion.aggregate planned expenditure is S5.5 trillion and unplanned inventory change is-$3.0 trillion.When real GDP is $5.0 trillion,aggregate planned expenditure is $6.5 trillion and unplanned inventory change is-$1.5 trillion.When real GDP s $7 5 trillion ag And when real GDP trillion and unplanned inventory change is$15 trillion. 2)Equilibrium expenditure occurs when unplanned inventory change is $0,or,equivalently,when real GDP equals aggregate planned expenditure.In this problem,equilibrium expenditure occurs when real GDP is $7.5 trillion. Consumption Government Real GDP,Y expenditure. Investment,I purchases,G (billions of 96(billions of 1996(billions of 1996(billions of1996 dollars) dollars) dollars) dollars) 100 150 150 150 200 200 150 150 300 250 150 150 400 300 150 150 500 350 150 150 600 400 150 150 700 450 150 150 80 500 150 150 900 550 150 150 三、论述题：20分（每小题10分） 得分 Answer:
2 Q Q 2 1 24 2 . 2.Answer: 1) When real GDP is $0, aggregate planned expenditure (the sum of C + I + G + X M) equals $4.5 trillion and unplanned inventory change (the difference between GDP and aggregate planned investment) is $4.5 trillion. When real GDP is $2.5 trillion, aggregate planned expenditure is $5.5 trillion and unplanned inventory change is $3.0 trillion. When real GDP is $5.0 trillion, aggregate planned expenditure is $6.5 trillion and unplanned inventory change is $1.5 trillion. When real GDP is $7.5 trillion, aggregate planned expenditure is $7.5 trillion and unplanned inventory change is $0. And when real GDP is $10 trillion, aggregate planned expenditure is $8.5 trillion and unplanned inventory change is $1.5 trillion. 2) Equilibrium expenditure occurs when unplanned inventory change is $0, or, equivalently, when real GDP equals aggregate planned expenditure. In this problem, equilibrium expenditure occurs when real GDP is $7.5 trillion. Real GDP, Y (billions of 1996 dollars) Consumption expenditure, C (billions of 1996 dollars) Investment, I (billions of 1996 dollars) Government purchases, G (billions of 1996 dollars) 100 150 150 150 200 200 150 150 300 250 150 150 400 300 150 150 500 350 150 150 600 400 150 150 700 450 150 150 800 500 150 150 900 550 150 150 三、论述题：20 分（每小题 10 分） 得分 1. Answer:
Price(dollars per unit) MC ATC MR D 0 Quantity(units per hour) The completed figure is above. Price and cost(dollars per meal) 20.00 MC ATC 16.00 12.00 8.00 4.00 MR 0 20 40 60 80100 Quantity(meals per day) 2.Answer: The basic idea of the multiplier is that any increase in expenditure will increase real GDP by a larger(a multiple)amount.The magnitude of the multiplier basically depends on how strongly consumers respond to additional income.Any initial increase in expenditure increases aggregate expenditure, which leads to more production and an increase in real GDP and income.Thus an increase,say in investment,will generate an increase in income and this increase,in turn,will induce an increase in consumption expenditure.The second round,the increase in consumption expenditure,is the result of the first round,the increase in investment.But the story does not stop with just two rounds.The initial increase in expenditure sets off a chain of increases because the second round increase in consumption leads to yet another increase in GDP and income.As a result of this next increase in income, consumption expenditure increases another time and a third round of expenditure increases occurs.The final result of all the rounds has real GDP increasing many fold compared to the initial increase in investment. 3
3 0 D M R M C ATC Quantity (units per hour) Price (dollars per unit) Q P The completed figure is above. Price and cost (dollars per meal) Quantity (meals per day) 0 20.00 16.00 12.00 8.00 4.00 20 40 60 80 100 M R D M C ATC 2. Answer: The basic idea of the multiplier is that any increase in expenditure will increase real GDP by a larger (a multiple) amount. The magnitude of the multiplier basically depends on how strongly consumers respond to additional income. Any initial increase in expenditure increases aggregate expenditure, which leads to more production and an increase in real GDP and income. Thus an increase, say in investment, will generate an increase in income and this increase, in turn, will induce an increase in consumption expenditure. The second round, the increase in consumption expenditure, is the result of the first round, the increase in investment. But the story does not stop with just two rounds. The initial increase in expenditure sets off a chain of increases because the second round increase in consumption leads to yet another increase in GDP and income. As a result of this next increase in income, consumption expenditure increases another time and a third round of expenditure increases occurs. The final result of all the rounds has real GDP increasing many fold compared to the initial increase in investment