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Problem Set 6. Competitive Market
EconS 526
1. Farmers produce corn from labor, a variable input, and land, a fixed input. The labor cost in
dollars to produce y bushels of corn is 𝑐𝑐(𝑦𝑦) = 𝑦𝑦 2 . There are 100 identical farms which all behave
competitively.
a. What is the individual farmer’s supply equation of corn?
In equilibrium price is equals marginal cost so, 𝑝𝑝 = 2𝑦𝑦. Therefore, we have 𝑦𝑦 = 0.5𝑝𝑝.
b. What is the market supply of corn?
π‘Œπ‘Œ = π‘šπ‘šπ‘šπ‘š = 100 βˆ— 0.5𝑝𝑝 = 50𝑝𝑝
c. Suppose the demand curve of corn is 𝐷𝐷(𝑝𝑝) = 200 βˆ’ 50𝑝𝑝. What is equilibrium price and
quantity of corn? How much does each individual firm produce?
We have supply equals demand 50𝑝𝑝 = 200 βˆ’ 50𝑝𝑝. Therefore, p=2 and Y=100. Since p=2, each firm only
produces y=1.
d. Assume that the market price you calculate in (c) is the long run equilibrium price. What is
the equilibrium rental value of land?
Each firm will have profit equal to zero. So, if total revenue is py = 2 and labor cost is 1 then rental rate
of land is 1 for profit equal to zero.
2. On a tropical island there are 100 boat builders, numbered 1 through 100. Each builder can build
up to 12 boats a year and each builder maximizes profit given the market price. Let y denote the
number of boats built per year by a particular builder. The cost function for boat builder i is
𝑐𝑐(𝑦𝑦) = 11 + 𝑖𝑖𝑖𝑖 such that the first builder has a cost function 𝑐𝑐(𝑦𝑦) = 11 + 1𝑦𝑦, the second
builder has a cost function 𝑐𝑐(𝑦𝑦) = 11 + 2𝑦𝑦, etc. Assume that the quasi-fixed cost $11 is only
paid id the firm produces a positive amount of output. If the price of boats is 25, how many
builders will choose to produce a positive amount of output? If the price of boats is 25, how
many boats will be built per year in total?
Firms will enter as long as positive profit is made. The first up to the 24th boat builder will make positive
profit. The 25th builder can cover variable cost but not the quasifixed cost so the builder will not build.
Therefore, 24 builders will enter the market. Each will produce a maximum of 12 boats. Note that given
linear cost, each firm only has an option to produce 0 or a maximum of 12. Therefore there will be 288
boats created (12x24).
3. US consumers have a demand function for umbrellas which has the form 𝐷𝐷(𝑝𝑝) = 90 βˆ’ 𝑝𝑝.
Umbrellas are supplied by US firms and UK firms. For simplicity, assume that there is a single
representative firm in each country that behaves competitively. The cost function for producing
umbrellas is given by 𝑐𝑐(𝑦𝑦) = 0.5𝑦𝑦 2 in each country.
a. What is the aggregate supply function for umbrellas?
Each individual firm maximizes profit such that p=y so individual supply is y=p. Therefore aggregate
output for two firms is Y=p+p = 2p.
b. What is the equilibrium price and quantity sold?
Supply equals demand so 2p= 90 –p. Therefore, p=30 and Y = 60.
c. Now the domestic industry lobbies for protection and Congress agrees to put a $3 tariff on
foreign umbrellas. What is the new U.S. price for umbrellas paid by the consumers?
The aggregate supply will change Y = p + (p-3). So demand equals supply is now 90-p=2p-3 so that p =
31.
d. How many umbrellas are supplied by foreign firms and how many are supplied by domestic
firms?
US will provide (y=p) 31 while UK provides (y=p-3) 28.
Deadline: November4, 2015 beginning of class. See syllabus for penalty due to late submissions.