ECON20120/30320 Mathematical Economics I EXAM 2023/24 (term 1)
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ECON20120/30320
Mathematical Economics I
EXAM 2023/24 (term 1)
Instructions
This part contains several questions to be completed before the dead- line. Your solution has to be uploaded to Blackboard. Your answer has to be typed (not hand-written!). If you would like to add igure or graphs, you are permitted to draw these by hand and paste into your answer. Please submit one single PDF document on Blackboard.
You should carefully explain the reasoning behind your answers and calculations. Be advised that the examiners attach considerable im- portance to the clarity with which answers are expressed. Show all the steps of your argument or calculation in your answer.
The irst 3 questions in your submission will be marked. If you submit solutions to all 4 questions, the last one on your submission will not be looked at. All questions have equal marks.
Answer three questions. Each question carries equal marks. Question 1
Consider the choice space f1, 2, 3, 4g with 4 elements. How many diferent preferences can be deined on this choice space?
Your answer has to be written in a structured way, i.e., explain how these diferent preferences can be derived without simply writing each and everyone of these down.
Form a hypothesis (i.e., outline your ideas but do not provide a proof) in the case that the choice space contains 5 elements.
[HINT: Do not believe everything you ind on the internet!]
Question 2
Consider the “mistrust” minimization problem
where is afunction, p1 , ..., pn are the prices of activities (per unit) and w is the budget. Real-world background story: By carrying out joint activities, trust between two people can increase and, thus, mistrust is reduced. The function S gives scores to a set of activities based on which and how often these are carried out.
(1) Prove that the function M(p,w): is quasi-concave.
(2) Can you give conditions such that M (p, w) is strictly quasi- concave?
[Hint: the subscript “+” means that all elements of a vector are non-negative and at least one element is strictly larger than zero.]
Question 3
Consider the relationship x y if and only if x2 ≥ y. What is the largest choice set (a subset of the real numbers ] [) such that deines a preference? Show all details of your claim and its proof.
HINT: There is an‘easy’answer and a more sophisticated one. Try inding both.
Question 4
Consider a project that runs over n + 1 periods with payments x0 , x1 , ...., xn. The present value at some interest rate r ≥ 0 is
Deine the external rate of return r* (x) as the largest(!) interest rate r ≥ 0 such that PV (x, r) = 0.
(1) Find conditions on the set of projects such that the external rate of return r* (x) exists.
(2) Find conditions on the set of projects such that the function
is quasi-concave.
Instructions: In (1) and (2), your conditions have to be as general as possible. Once you have written down some conditions and proved that these are sufficient,illustrate why it is difficult to make these conditions more general (e.g., with counterexamples). Show all the steps of your argument or reasoning!
2024-01-25