Question 2: [40 points] Consider Bertrand competition with homogeneous products.
ID: 1193135 • Letter: Q
Question
Question 2: [40 points] Consider Bertrand competition with homogeneous products. Two firms, 1 and 2, produce an identical product and compete by choosing price. Consumers buy from the firm with the lower price. If the prices are identical, however, assume all consumers buy from firm 1. Inverse demand for the product is given by Q = 80 P and each firm has a marginal cost of 10. Assume that the firms can only set integer prices, so if one wants to undercut the other by the smallest amount possible, the undercut must be at least a dollar.
(a) [10 points] Write out the best response function of firm 1 for any price that firm 2 could choose. 1
(b) [10 points] Write out the best response function of firm 2 for any price that firm 1 could choose.
(c) [20 points] What is/are the Nash equilibrium/equilibria of this game?
Explanation / Answer
Q = 80 - P
MC1 = 10
MC2 = 10
(a) For firm 1,
Q1 = 80 - P1 - P2
TR1 = P1 x Q1 = 80P1 - P12 - P1P2
TC1 = MC1 x Q1 = 10 x (80 - P1 - P2) = 800 - 10P1 - 10P2
Profit for firm 1, Z1 = TR1 - TC1
= 80P1 - P12 - P1P2 - 800 + 10P1 + 10P2
= 90P1 + 10P2 - P12 - 800 - P1P2
Profit is maximizined when dZ1 / dP1 = 0
90 - 2P1 - P2 = 0
2P1 + P2 = 90 (1) [Firm 1's response function]
(b) For firm 2,
Q2 = 80 - P1 - P2
TR2 = P2 x Q2 = 80P2 - P1P2 - P22
TC2 = MC2 x Q2 = 10 x (80 - P1 - P2) = 800 - 10P1 - 10P2
Profit for firm 2, Z2 = TR2 - TC2
= 80P2 - P1P2 - P22 - 800 + 10P1 + 10P2
= 90P2 + 10P1 - P22 - 800 - P1P2
Profit is maximizined when dZ2 / dP2 = 0
90 - 2P2 - P1 = 0
P1 + 2P2 = 90 (2) [Firm 2's response function]
(c) Nash equilibrium is found out by solving equations (1) & (2):
2P1 + P2 = 90 (1)
(2) x 1 gives us: 2P1 + 4P2 = 180 (3)
3P2 = 90
P2 = 30
P1 = 90 - 2P2 [from (2)]
= 90 - (2 x 30) = 90 - 60 = 30
So, Q = 80 - (30 + 30) = 20
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