In: Economics
QD=40-2P and QS=P-8 represent market
demand and supply functions for a good. If each unit of the good
produced involves external costs of $4 (i.e. MEC=4), then
(a) what amount of good is produced in the market
equilibrium?
(b) What are marginal social benefits(MSB) and marginal social
costs (MSC) at the market equilibrium quantity?
a) QD =40 -2P
=> P = (40 - Q) / 2
=> P = 20 - 0.5Q
=> Marginal private benefit: (MPB) = 20 - 0.5Q
QS = P -8
=> P = Q + 8
=> Marginal private cost: (MPC) = Q +8
At market equilibrium, MPB = MPC
=> 20 - 0.5Q = Q + 8
=> 20 - 8 = Q + 0.5Q
=> 12 = 1.5Q
=> Q = (12 / 1.5)
=> Q = 8
8 units of good is produced in the market equilibrium.
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(b) Marginal social benefit (MSB) = Marginal private benefit (MPB) + Marginal External benefit (MEB)
note: MEB = 0
=> MSB = MPB + 0
=> MSB = 20 - 0.5Q
Put Q = 8
=> MSB = 20 - 0.5 (8)
=> MSB = 16
Marginal social benefit at market equilbrium quantity is 16
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Marginal social cost (MSC) = MArginal private cost (MPC) + Marginal external cost (MEC)
=> MSC = Q + 8 + 4
=> MSC = Q +12
Put Q = 8
=> MSC = 8 +12
=> MSC = 20
marginal social cost at the market equilibrium quantity is 20.