A firm has the following (long-run) cost function: TC(Q)=Q^3-10Q^2+100Q. Suppose the market demand is given by Q=200-P, and all firms have identical cost functions. How many firms are present in the market.
The long-run price is equal to the minimum average total cost.
The minimum of average total cost output is found by differentiating the ATC function and equating to the zero.
ATC=TC/Q=Q^2-10Q+100
dATC/dQ=2Q-10
equating to zero
2Q-10=0
2Q=10
Q=5
P=ATC=5^2-10*5+100
=75
The price is $75
the quantity demanded by the market at a price is found by the demand curve
Q=200-75=125
Number of firms =market quantity/individual firms quantity
=125/5
=25
25 firms are present in the market.
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