Question

2. Skip and Peggy are brother and sister and they fight about everything. Skip says that perfectly competitive firms maximize profit where marginal revenue equals marginal cost. Peggy says perfectly competitive firms maximize profit where price equals marginal cost. Settle this sibling rivalry once and for all.

Answer 1

Answer: They are both right.

Explanation:

Firms in every market will always maximise profit where their Marginal Revenue equals Marginal Cost because at this point, resources are being fully utilized. This is therefore no different in a Perfectly competitive market so Skip is correct.

Peggy is also correct however because in a Perfectly Competitive market, the demand curve is perfectly elastic. This creates a situation where the Price, Marginal Revenue and Average Revenue are all the same and represent the demand curve as well.

With the Price being the same as the Marginal Revenue in a Perfectly competitive firm, that means that where the Price equals Marginal Cost is where the Marginal Revenue equals Marginal Cost as well so indeed perfectly competitive firms maximize profit where price equals marginal cost.