# 想請問一些經濟考古題??

1. Suppose that the demand curve is given by D(p) = 10 - p. If the price changes

from 4 to 6, what is the change in consumer's surplus?

2. If a firms faces elastic demand, an increase in the price of its output may increase

its revenues; true or false?

3. If the demand curve facing the monopolist has a constant elasticity of s, then what

will be the profit-maximization monopolist's markup on marginal cost?

4. A monopolist never produces where the demand for output is inelastic, true or

false?

5. Suppose that there are two firms that face a linear demand curve p(Y) = a - bY and

have constant marginal costs, c, for each firm. Solve for the Cournot equilibrium

output for each firm and the equilibrium price.

6. State the characteristics of monopolistic competition, and the long-run equilibrium

condition(s) for a representative firm in the monopolistic competition market.

Rating

1. Q = 10 - P，P = 4 → Q = 6；P = 6 → Q = 4

弧彈性|Ed| = - [(4 - 6)/(4 + 6)]/[(6 - 4)/(6 + 4)] = -(-1) = 1

2. False！

需求有彈性 → |Ed| > 1

價格和總收入的關係︰dTR / dP = Q (1 - |Ed|)，而 Q > 0，|Ed|>1 ，所以 Q (1 - |Ed|) = dTR / dP < 0 → 價格和總收入成反向

所以價格上升，總收入下降。

3. constant大概是單一彈性吧，|Ed| = 1代入下面

MR = dTR / dQ = P (1- 1 / |Ed|) = 0 = MC，此時 MR = MC = 0

4. True！

獨占Max π時，會讓 MR = MC

所以MR要大於 0 → MR = dTR / dQ = P (1 - 1 / |Ed|) > 0

P > 0，所以 |Ed| < 1(inelastic)，才會讓 P (1 - 1 / |Ed|) = MR > 0

5. 假設Y = Y1 + Y2

其中之一廠商利潤π1= TR1 - TC1 = P．Y1 - cY1 = [a - b(Y1+Y2)]Y1 - cY1 = (a - bY1 - bY2)Y1 - cY1 = aY1 - bY12 - bY2Y1 - cY1

dπ1 / dY1 = a - 2bY1 - bY2 - c = 0

MC相同，產量相同，Y1 = Y2，所以 a - c - 2bY1 - bY1 = a - c - 3bY1 = 0 → Y1 = Y2 = (a - c) / 3b

Y = Y1 + Y2 = 2(a - c) / 3b，P = a - 2b(a - c)]/3b = a - (a - c)/b

6.

MR = LMC = SMC

AR = LAC = SAC

MR < AR = P

2009-04-08 22:21:02 補充：

5. 的 bY12 是 bY1平方

Source(s): ME, ME