,,
(a) QA (associated with point A).
(b) QB (associated with point B).
(c) QC (associated with points C1 and C2).
(d) QE (associated with point E).
Feedback:
(a) Competitive firms strive for the rate of output at which marginal cost (MC) equals
price—here at point A, where market price is determined by the intersection of the
industry supply (MC curve) and demand curve. When a competitive market reaches this
rate of output, short-run equilibrium is achieved. Recall that Demand = Marginal
Revenue = Price for competitive firms.
(b) If the short-run equilibrium is profitable (p > ATC), other firms will want to enter the
industry. As they do, market price will fall until it reaches the minimum level of the
average total cost curve at point B. In this long-run equilibrium for the perfectly
competitive market, economic profits are zero and no additional firms want to enter or
exit the industry.
(c) The profit-maximizing rate of output for a monopoly occurs where the marginal cost
and marginal revenue curves intersect (point C1). The demand curve associated with this
level of output indicates the price (point C2) that consumers will pay. Barriers to entry
prevent other firms from entering this monopolistic market; therefore a monopolist’s
demand curve will never shift left.
(d) For monopolistic competition, in the long run more firms enter the industry. As they
do so, the demand curve facing each firm shifts to the left as all market shares decline.
Firms still equate MR and MC. Ultimately, long-run equilibrium will be found where the
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