The MR = MC rule applies

A) in the short run but not in the long run.
B) in the long run but not in the short run.
C) in both the short run and the long run.
D) only to a purely competitive firm.

MR = MC Rule

An economic principle stating that profit maximization occurs when a firm's marginal revenue equals its marginal cost.

Short Run

In economics, a timeframe during which the quantity of at least one production factor cannot be increased.

Long Run

A period in which all factors of production and costs are variable, allowing for full adjustment to changes in market conditions.