Final answer:
The marginal product of the second worker is six units, as the use of a two-person saw increases efficiency when operated by two workers.
Step-by-step explanation:
The marginal product of the second worker is the additional output produced by the employment of that worker. According to the information provided, if zero workers produce zero units and the marginal product of the first worker is four units, then the marginal product of the second worker, working with a two-person saw, is an additional six units. This increase in output to six units from four can be attributed to the efficient use of capital when two workers operate the equipment designed for two people, making the overall process more productive.
The concept of marginal product is important when examining the efficiency of labor in relation to capital within a production process. As more workers are added, the marginal product may increase if they complement the existing capital effectively, but it may also decrease due to factors such as limited capital or diminishing returns.