Solutions to ECON6001 final, S2 2019
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Solutions to ECON6001 final, S2 2019
1 Multiple Choice Questions (20 points)
1. Consider a game with the following tree.
How many strategies does player 2 have?
(a) 7
(b) 10
(c) 12 (***)
(d) None of the above.
2. Consider the game tree from question 1. Which of the below is an SPNE of this game?
(a) (X ; (a|X, b|Y, c|Z))
(b) (X ; (a|X, a|Y, b|Z))
(c) (X; a)
(d) None of the above. (***)
3. Consider the following game.
|
L |
C |
R |
T |
U |
3,2 |
-5,7 |
8,3 |
1,-1 |
M |
4,1 |
3,-2 |
3,3 |
2,5 |
D |
1,3 |
-2,-2 |
1,2 |
2,3 |
How many pure strategy Nash equilibria does this game have?
(a) 0
(b) 1
(c) 2 (***)
(d) None of the above.
Consider the following set-up for questions 4 and 5:
Suppose that there are four types of car quality: lemons, grapefruits, or- anges and peaches. Probability distribution of cars in the economy is as follows: P (L) = , P (G) = , P (O) = and P (P) = . The correspond- ing values for the seller are $1, 000, $1, 200, $1, 800 and $2, 000, whereas values for the buyer are $1, 200, $1, 400, $2, 000 and $2, 200. Suppose the price of a random car on the market is p = $1, 600.
4. What kinds of the cars will be offered in the market?
(a) Lemons
(b) Lemons and grapefruits (***)
(c) Lemons, grapefruits and oranges
(d) All cars
5. What is the expected value to the buyer of a random car priced $1,600?
(a) $666.67
(b) $1,333.33 (***)
(c) $1,700
(d) None of the above.
6. Consider a production technology that depends on capital K and labor L: f(K, L) = KL. A firm with this technology would choose to use the following amount of capital:
(a) +∞ (***)
(b)
(c)
(d) None of the above.
7. Suppose a consumer evaluates the AA acts as the worst prize that the act pays and ignores the actual distribution of probabilities. Formally, the value of an act f is V (f) = min{z : f(s)(z) > 0}, where f(s)(z) is probability of prize z in state s. Consider the following statements:
I. V (f) represents an MEU preferences.
II. Preferences represented by V (f) are complete. Which of the above statements are correct?
(a) I only
(b) II only (***)
(c) I and II
(d) None
8. Which utility function represents the same preferences as u(x, y) = 2x2 +y?
(a) 2x + y
(b) x2 y
(c) −e2x2 +2y
(d) None of the above. (***)
9. What returns to scale does production function f(K, L) = max(K, K +L) exhibits?
(a) DRS
(b) CRS (***)
(c) IRS
(d) None of the above.
10. Which of the below statements is false?
(a) Marshallian demand is homogenous of degree 0 in (p, I)
(b) Indirect utility is homogenous of degree 0 in (p, I)
(c) Expenditure function is homogenous of degree 0 in p (***)
(d) None of the above.
2 Long Answer Question (20 points)
Suppose there are two firms in the market with different marginal costs MC1 = 1 and MC2 = 2. Market demand is Q = 200−P . The firms participate in Cournot oligopoly.
1. What is the equilibrium quantities of each firm, price, profits and consumer surplus? (10 points)
Solution: Consider firm 1 first:
max(200 − q1 − q2 )q1 − q1
1
FOC: 200 − 2q1 − q2 − 1 = 0
199 − 2q1 − q2 = 0
Consider firm 2:
max(200 − q1 − q2 )q2 − 2q2
2
FOC: 200 − 2q2 − q1 − 2 = 0 ⇒ q1 = 198 − 2q2
By plugging q1 into FOC of firm 1, we obtain
199 − 2(198 − 2q2 ) − q2 = 0 ⇒ q2 = ≈ 65.67
q1 = 198 − 2q2 = ≈ 66.67
P = 200 − q1 − q2 = ≈ 67.67
π 1 = 67.67 × 66.67 − 66.67 ≈ 4, 444
π2 = 67.67 × 65.67 − 2 × 65.67 ≈ 4, 312
CS = 0.5 × (200 − 67.67) × (65.67 + 66.67) ≈ 8, 756.
2. Define the efficient market price and quantity. Calculate DWL. (4 points)
Solution: The most efficient firm is firm 1, so competitive price PC = MC1 = 1 and the competitive total quantity would be QC = 200−1 = 199. Firms will be earning zero profit: πC = 1 × q − 1 × q = 0. Hence, the total surplus would be equal to consumer surplus:
CSC = 0.5 × 199 × (200 − 1) = 19, 800.5
DWL = CSC − CS − π 1 − π2 ≈ 2, 288.
3. Now consider 3 firms with the same marginal costs MC = 1. However, now the game is sequential. In period 1, two firms simultaneously choose their output. In period 2, the third firms observes output produced by other firms and then chooses its own production. Find the equilibrium quantities and price. (6 points)
Solution: By using backward induction, we start with firm 3:
max(200 − q1 − q2 − q3 )q3 − q3
3
FOC: 200 − q1 − q2 − 2q3 − 1 = 0 ⇒ q3 = 0.5(199 − q1 − q2 ).
Now we turn to firms 1 and 2 and take into account how firm 3 will choose
its production:
max(200 − q1 − q2 − 0.5(199 − q1 − q2 ))q1 − q1 = 0.5(199 − q1 − q2 )q1
1
FOC: 0.5(199 − 2q1 − q2 ) = 0
Similarly for firm 2, we will have
199 − 2q2 − q1 = 0 ⇒ q1 = 199 − 2q2 .
By plugging q1 into FOC of firm 1, we obtain
199 − 2(199 − 2q2 ) − q2 = 0 ⇒ q1 = q2 = ≈ 66.33 q3 = 0.5(199 − q1 − q2 ) = ≈ 33.17 P = 200 − q1 − q2 − q3 = ≈ 34.17.
2022-05-21