In the short run, perfectly (or purely) competitive firms will maximize their profit by producing: the quantity where marginal revenue = marginal cost and where quantity when the price = marginal cost.
A perfectly competitive firm is a theoretical market structure when all firms sell the same product where there is no influence on the price that consumers pay. Marginal revenue is the additional revenue that a company earns by increasing their production by one more cost. Marginal cost refers to the cost added by producting one more product.
