MATH 331 FEBRUARY 2022 CLASS TEST GAME THEORY
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MATH 331
FEBRUARY 2022 CLASS TEST
GAME THEORY
1. a) A rustic poker game for two players, and , begins with both players staking £2 into the kitty. In this game there is a hat containing six cards, one marked with the number ‘1’, four marked with the number ‘3’ and one marked with the number ‘5’. The game starts with Player selecting (at random) two cards from the hat (both players are careful not to show their cards to their opponent). Player then selects a single card from those remaining in the hat. Now Player must decide to call either “Raise £4” or “Raise £2”. He then adds either £4 or £2 into the kitty, depending on which call he makes. Now it is player B’s turn. If he holds the ‘5’ card, his only option is to turn it face up and call “Stick”. But if he holds the ‘1’ or a ‘3’ card, then he may call either “Raise £2” or “Stick” as before. If calls “Raise £2”, then he pays £2 into the kitty and selects a second card from the hat.
At this point the game concludes, the players turn over all the cards they hold in their hands. The winner of the game is the player with the higher score. A player’s score is given by the total numbers on their respective card/s, minus the money they paid into the kitty to obtain those cards. The player with the higher score wins all the money in the kitty. If the scores are equal, the kitty is shared.
Draw a game tree for this game, including the information sets, the relevant probabilities ofthe possible scenarios and the monetary payoffs the players receive. To simplify the diagram:
i) Show all of ’s information sets, but only those for when he first selects either the ‘1’ or ‘5’ card.
ii) Compute and show the payoffs only in those instances when player calls “Raise £4”.
[11 marks]
b) Compute the total number of playing strategies for each player. Write out any three of Player ’s playing strategies in full. Do the same for any three of Player ’s playing strategies.
[4 marks]
c) Suppose both players adopt their most aggressive playing strategies, that is Player calls “Raise £4” in all circumstances and Player calls “Raise £2” whenever permissible. Calculate the expected payoff for both players ifthese two strategies are pitted against one another.
[5 marks]
2. a) In a 2 × 2 strategic game, the payoff bi-matrix for the two players A (row) and B (column) is given by
().
Using the swastika method, or otherwise, find the Nash equilibria ofthe game. [8 marks]
b) A more general version ofthis particular 2 × 2 strategic game, is defined by the following payoff bi-matrix
(),
where and ∈ ℝ . Establish the conditions on and that ensure the game contains a Nash equilibrium point over the mixed strategies.
[6 marks]
c) Assume that the game b) above contains a Nash equilibrium point over the mixed strategies ( , ). Write down an expression for , the sum of and ’s respective payoffs when plays and plays . If = 5⁄2, establish the value of , consistent with conditions found in part b), that maximises .
[6 marks]
3. a) A player has prospects 1, 2, 3 and 4 with 1 preferred to 4 . Suppose that
2~ [5 1, 3 4]
3~ [ 1, 4].
What is the preference relation between 2 and 3? The prospect s is such that
~ [1 2, 5 3] .
Find p such that
~[1, (1 − )4],
and q such that
2~[3, (1 − )4].
Is there an r such that 3~[2, (1 − )4]?
[1 mark]
[2 marks]
[2 marks]
[2 marks]
b) Let () be a Gambler’s utility of regarding the prospect of winning/losing £x. Suppose his utility scale is standardised by setting
(1000) = 1000 and (−100) = −100. The Gambler has staked £100 at the card table to play a particular card game. In this game a pack of 16 face cards (4 Aces, 4 Kings, 4 Queens and 4 Jacks) is used.
In round 1, the Dealer deals two cards face down to the Gambler. He then turns them over. If the two cards have the same face (2 Aces, 2 Kings, 2 Queens or 2 Jacks), then the Gambler can either call “Raise” or “Stick”. If he calls “Stick” he is awarded a prize of £500. Ifthe cards are different, he loses his stake money.
Round 2 commences ifthe Gambler calls “Raise” . The Dealer shuffles the remainder of the pack and deals two further cards face to the Gambler. He then turns them over. If the two new cards match his two earlier face cards (so he now holds 4 Aces, or 4 Kings etc.) then he wins a £100,000 prize. Ifthe two new cards have the same face but differ from his original two cards (e.g. he picks up 2 Aces, then 2 Kings, etc.) he wins a £1000 prize. Otherwise he loses his stake money.
Suppose the Gambler adopts the strategy of calling “Raise” whenever he can. Establish the probability of the Gambler losing his stake money in the game pursuing this strategy.
[8 marks]
For the Gambler the prospect of 500 is ten times more valuable than playing the game. But he values the prospect of playing the entire game 50% higher than the prospect ofjust playing round 1 and then stopping by calling “Stick” . Assuming EUP, calculate the values of (100,000) and (500) on the Gambler’s utility scale.
[5 marks]
2022-03-19