ECON30020 Final Exam 2021
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
ECON30020
Final Exam
2021
Problem 1: Concave and convex functions and their inverses Let
f : X → Y with X S R and Y S R be a function whose inverse f -1 (y) exists and is denoted g(y), that is, g(y) = f -1 (y). a) Assume first that f is twice differentiable, that is, f\ and f\\ exist, and that f\ 0 everywhere. Under what condition does strict convexity of f imply strict convexity of g, and under what conditions does strict convexity of f imply strict concavity of g? [10 Points]
b) Now drop the assumptions of differentiability. Do the results above ex- tend? Your explanation may be formal or verbal. [10 Points]
Problem 2: Monopoly pricing Consider a monopoly seller who faces the
inverse demand function
P (Q) =
if Q e [0, 4]
if Q e (4, 16] .
(1)
Suppose the seller has a quantity of 4 for sale, that is, the cost of producing (or selling) a quantity of 4 or less is zero, and selling any larger quantity is prohibitively costly (or simply impossible). Find the revenue maximizing two-price mechanism for selling these 4 units. Say also how much revenue the monopoly makes using this two-price mechanism, and how much revenue
it would make if it were required to set a single price. [20 Points]
Problem 3: Linear algebra
a) Find the inverse of the matrix A = ╱ 1(3) 2(4) ← . [8 points]
b) For the transition probability matrix
P = ╱ ( 0 |
0 0.5 0.8 |
、 0.2 . , |
whose entries pij give the probability of moving from state i into state j ,
find the stationary distribution x = .(、) , which satisfies xT P = xTand
i(3)=1 xi = 1. [12 Points]
Problem 4: Cost minimization Assume a continuum of consumers are uniformly distributed along the interval [0, 1]. A social planner chooses the placements of n e {1, 2} “shops” . Consumers have linear transportation costs and visit the shop that is closest to their location.
a) For n = 1 and n = 2, derive the transportation costs minimizing place- ments, and the minimum cost associated with each of these. Check the second-order conditions as well. [12 Points]
b) Suppose now that setting up the second shop comes at a cost k > 0, determine as a function of k under what conditions the social planner would set up n = 2 shops and when only 1 shop, assuming that the planner aims to minimize the sum of consumers’ transportation costs and the cost of setting up shops. (Assume that setting up the first shop has 0 costs.) [8 Points]
Problem 5: Stagecoach problem Consider the variant of the stagecoach problem displayed in Figure 1 for a travelling business man who has to go from A to J. The traveller can only move from left to right, so from A he can go to B, C or D and from each of these locations to either E, F or G, and from each of these to either H or I, and then from there to J. The costs for each leg of the journey are displayed in the four tables below, whose entries ahk give the cost from travelling from h to k . Find the minimum cost from traveling from A to J and say which route(s) minimize the cost of travelling from A to J. Is there a unique cost minimizing route?
In your working, denote by V (X) the minimum cost from point X on- wards and by a(X) the optimal action(s) at point X, using lower case letters to indicate an action, e.g. a(X) = y means that at X one travels to Y . [20 Points]
B |
C |
D |
A 4 |
3 |
2 |
|
E |
F |
G |
B |
5 |
6 |
1 |
C |
2 |
8 |
4 |
D |
3 |
9 |
10 |
H I |
||
E |
2 |
3 |
F |
4 |
5 |
G |
1 |
2 |
J |
H 4 |
I 2 |
2022-06-18