Comment on the problem with this statement: “Of course, there are diminishing marginal returns from adding more workers to a fixed quantity of plant and equipment because additional workers are not as good as initial workers.”

Please provide the best answer for the statement.

The law of diminishing returns assumes all units of variable inputs, which would be workers in this case, are of equal quality. Marginal product diminishes not because each additional worker who is hired is inferior to the previous worker, but because more workers are being used relative to the fixed plant and equipment that is available. Sunk costs should be disregarded in decision making.