Department of Economics, University of Oslo
Seminar – autumn 2005
Note: exercise 1 will be discussed at the first seminar.
Exercise 1
A. Consider a utility-maximising consumer with a given set of preferences and a budget
who faces given market prices. Make assumptions on preferences that will ensure a
unique solution to the consumer’s choice problem. Discuss how the choice of the
consumer depends on the levels of
the budget,
B. Consider next a profit-maximising firm facing a price sensitive demand for its product.
Characterise the optimal output decision of the firm. Discuss how the choice of the firm
depends on
the level of demand,
the slope of the demand curve,
Exercise 2
A. Explain what we mean by ‘an act’, ‘a state of the world’, ‘the probability of a state’ and
‘an outcome’. Discuss the reasonableness of assuming that a decision maker (i)
knows the set of states and (ii) is able to assign probabilities to each of the possible
B. What is the Expected Utility Theorem? Explain the assumptions underlying this result
and discuss their reasonableness.
C. Explain what is meant by a decision maker being, respectively, ‘risk averse’, ‘risk
loving’ and ‘risk neutral’. What is the mathematical characterisation of a utility function
which represents, respectively, risk aversion, risk attraction and risk neutrality.
D. What attitude towards risk is implied by the following utility functions:
u ( x ) = ln x
u ( x ) = ex
u ( x ) = a + bx , where a and b are positive constants.
u ( x ) = x2
E. Consider the utility function u ( x ) = a + bx + cx . What assumptions have to be
made on this function for it to represent risk averse agent who derives utility from x? Is
the function valid for any value of x?
Exercise 3
A farmer has at his disposal 100 acres of land. The land may be used for growing wheat
or barley. The wheat yield depends on the weather (i.e. occurrence of frost), while the
barley yield does not. Consequently, if the weather is good the farmer receives a yield on
wheat land worth NOK 4500 per acre, whereas if the weather is bad the value of the
wheat crop is NOK 1500 per acre only. The probability of bad weather is 1/3. The yield on
barley is NOK 2500 in any case. Irrespective of the choice of crop, the cost of fertilisers,
seeds etcetera is NOK 1000 per acre.
A. Assume the farmer choose to produce wheat only. Show that in this case his expected
net income equals NOK 250,000.
B. If the farmer only considers the two extremes, ‘all barley’ and ‘all wheat’, should he then
choose all wheat? Explain!
C. Assume the farmer has preferences that satisfy the Expected Utility Theorem and that
his (von Neuman Morgenstern) utility function is u ( x ) , where x is net income. What are
the expressions for the farmer’s expected utility in the two cases considered in B?
D. Assume now that the farmer may choose a mix between wheat and barley. Let Y
denote the amount of land used for barley. Net income in good weather conditions is
denoted xG while net income in bad weather conditions is xB . Show that
xG = 350, 000 − 2000Y
xB = 50, 000 + 1000Y
E. Derive the expression for the farmer’s expected utility and show how it depends on Y.
Explain how we may (in principle) find the optimal value of Y.
Exercise 4
We consider a firm that may invest in a project with a risky outcome. If the firm invests an
amount K, with probability p revenues are RH ( K ) and with probability 1-p revenues are
RL ( K ) , where RH ( K ) > RL ( K ) and both RH and RL are twice continuously
differentiable, increasing and concave.
In the first part of the exercise, we assume that the unit cost of investment is 1+r, where r
is the (given) interest rate.
A. Consider the case in which the firm acts as if it does not care about risk. What is the
expression for expected profits? Derive the first-order condition for the profit-maximising
investment level. Interpret the result.
B. Consider next the case in which the firm acts as if it is risk averse. Can you give
reasons for this assumption? Assume that the firm acts as if it evaluates profits according
to the utility function u. What is the expression for expected utility of the firm? Derive the
first-order condition for the expected-utility maximising investment level. Interpret the
result. How does the resulting investment level compare to that under A?
Suppose that the firm has access to two different sources of finance. In addition to being
able to borrow at the fixed interest rate r, the firm may also borrow at a risky rate ri . For
simplicity we assume that the interest rate ri takes on the value rH when revenues are
RH and the value rL when revenues are RL , where rH > rL .
C. Consider again the case of risk neutrality. Is it possible that the firm may choose to
borrow from both sources? Under what conditions on the interest rates will the firm choose
to borrow at the fixed and risky interest rate, respectively? Does the firm’s choice depend
on the riskiness of revenues?
D. Consider next the case of risk aversion. Explain why the firm would never borrow at the
fixed interest rate if r > rH . Explain also why the firm would never borrow at the risky
interest rate if r < rL . Suppose for the rest of the analysis that rL < r < rH . Is it
prH + [1 − p ] rL > r ? Does the choice depend on the riskiness of revenues? Explain.
We return again to the case in which the firm can borrow at a fixed rate of interest only.
However, we now assume that the profit of the firm is subject to a (proportional) tax t.
E. In the case of risk neutrality, does the rate of taxation affect investment behaviour?
F. What about in the case of risk aversion? Explain.
Exercise 5
A. (Gibbons, Problem 1.1) What is a game in normal form? What is a strictly dominated
strategy in a normal-form game? What is a pure-strategy Nash equilibrium in a normalform game?
B. (Gibbons, Problem 1.2) In the following normal-form game, what strategies survive
iterated elimination of strictly dominated strategies? What are the pure-strategy Nash
Player 2
Player 1
C. Clothes manufacturer A is reputed to be a trend setter. A’s competitor B aims at
customers who want the types of clothes sold by A but are willing to accept cheaper
copies if they exist. A has two different choices for the next collection. If A and B choose
different styles, A earns a payoff of 40 and B a payoff of 20. If both choose the same style,
A earns 20 and B 40. Formulate the normal-form representation of this game and find any
Nash equilibria.
D. (Varian, ch 28, Review question 2) Are dominant-strategy equilibria always Nash
equilibria? Are Nash equilibria alwas dominant-strategy equilibria?
E. (Varian, ch 28, Review question 3) Suppose your opponent is not playing his or her
Nash equilibrium strategy. Should you play your Nash equilibrium strategy?
F. (Varian, ch 28, Review question 4) We know that the single-shot prisoner’s dilemma
game results in a dominant Nash equilibrium strategy that is Pareto inefficient. Suppose
we allow the two prisoners to retaliate after their respective prison terms. Formally, what
aspect of the game would this affect? Could a Pareto efficient outcome result?
Exercise 6
A. (Cabral, Review and Practice Exercise 4.1) What are the assumptions regarding player
rationality implicit in solving a game by iterated elimination of dominated strategies?
Contrast this with the case of dominant-strategy solutions.
B. Cabral, Review and Practice Exercise 4.3.
C. (Gibbons, Problem 1.3) Players 1 and 2 are bargaining over how to split one dollar.
Both players simultaneously name shares they would like to have, s 1 and s 2 , where
0 ≤ s 1 , s 2 ≤ 1 . If s 1 + s 2 ≤ 1 , players receive the shares they named; if s 1 + s 2 > 1 , both
receive zero. What are the pure-strategy Nash equilibria of this game?
D. (Gibbons, Problem 1.8) Consider a population of voters uniformly distributed along the
ideological spectrum from left ( x = 0 ) to right ( x = 1 ). Each of the candidates for a single
office simultaneously choose a campaign platform (i.e., a point on the line between x = 0
and x = 1 ). The voters observe the candidates’ choices, and then each voter votes for
the candidate whose platform is closest to the voter’s position on the spectrum. If there are
two candidates and choose platforms x1 = 0.3 and x2 = 0.6 , for example, then all voters
to the left of x = 0.45 vote for candidate 1, all those to the right vote for candidate 2, and
candidate 2 wins the election with 55 per cent of the vote. Suppose that the candidates
care only about being elected – they do not really care about their platforms at all! If there
are two candidates, what is the pure-strategy Nash equilibrium? If there are three
candidates, exhibit a pure-strategy Nash equilibrium. (Assume that any candidates who
choose the same platform split the votes case for that platform, and that ties among the
leading vote-getters are resolved by coin flips). See H Hotelling, Stability in Competition,
Economic Journal, 39, 41-57, 1929, for an early model along these lines.
Exercise 7
A. Review and Practice Exercises 4.4, 4.5, 4.6 and 4.7 in Cabral.
B. Review Question 6 in Chapter 28 in Varian.
C. Problems 2.1 and 2.2 in Gibbons.
Exercise 8
A. Problems 2.10, 2.11 and 2.12 in Gibbons.
B. Review Question 1 in Chapter 28 in Varian.
C. Review and Practice Exercises 4.2 in Cabral.
D. Review Question 5 in Chapter 28 in Varian.
Exercise 9
A. Review and Practice Exercises 7.1-5 in Cabral.
B. Review and Practice Exercises 8.1 and 8.2 in Cabral.
C. Exam Autumn 2003
Exercise 10
(Exam Autumn 2003)
A. Define and explain the following terms: game, strategy, player, normal-form
representation, extensive-form representation, dominant-strategy equilibrium, Nash
B. Two firms are competing on a market. Each firm may choose one out of two possible
strategies; Aggressive and Accommodating. If both firms choose the Aggressive strategy
each earn zero profits; if both choose the Accommodating strategy each earn a profit of
100; if one firm choose the Aggressive strategy and the other the Accommodating
strategy, the first earns a profit of 200 and the second a profit of -100. Express the game
in normal form and solve it.
C. Consider a repeated version of the above game. Explain under what conditions both
firms always playing the Accommodating strategy may be supported as an equilibrium
D. Adam Smith wrote that “People of the same trade seldom meet together, even for
merriment and diversion, but the conversation ends in a conspiracy against the public, or
in some contrivance to raise prices”. Discuss conditions under which such a “conspiracy”
may be successful.