(3) Marginal Revenue = Marginal Cost Explanation: 173. (3) When the marginal revenue productivity of a factor is equal to the marginal- cost (MR=MC) of the factor, the firm will be in equilibrium and its profits maxmized. Equilibrium in perfect competition is the point where market demands will be equal to market supply. The condition that price equals both average revenue and marginal revenue (P = AR = MR) is the standard condition for a perfectly competitive firm.