Final answer:
The law of diminishing returns indicates that as more workers are added to a production process with fixed capital, the increase in output will decline, leading to diminishing marginal productivity.
Step-by-step explanation:
According to the law of diminishing returns, the result of adding more workers to the production process, given that all other factors stay the same, is that the diminishing marginal productivity becomes apparent. This is a general rule indicating that as a firm employs more labor, there is an initial increase in output, but this increase eventually declines. The marginal product of an additional worker will increase at first, but as more workers are added, it will start to decrease. This could even lead to no effect or a negative impact on production. This phenomenon is due to the fixed capital (like machinery and workspace), which remains constant while the number of workers increases.