Answer:
Even when competitive firms are unable to calculate marginal revenue product directly, competition in the labor market will push wage rates toward the marginal revenue product of labor.
Explanation:
The labor market is made up of employers seeking for labor and employees offering their labor services. The law of supply and demand also applies to this market, when more employers are seeking employees, the price (= salary) will increase.
For example, if many companies are making a profit and they need more labor, the salaries will rise because the demand is rising.
Also the suppliers, the potential employees, compete against each other for the best possible jobs.
