If a firm increases the use of labor while keeping capital constant, what happens to the marginal revenue product of labor if the inputs are substitutes?

When a firm increases the use of labor while keeping capital constant, the marginal revenue product of labor can change, especially if the inputs are substitutes. This means that as more workers are hired, each additional worker may contribute less to the firm's overall output because they have to share the same amount of capital. For example, imagine a factory with a fixed number of machines; if more workers are added, they might not all be able to use the machines efficiently, leading to diminishing returns. As a result, the value generated by each additional worker may decrease, which means the marginal revenue product of labor falls. Therefore, while increasing labor can initially boost productivity, too much labor without enough capital can lead to reduced efficiency.