How can there be such a thing as a marginal revenue or cost curve when they use discrete variables, i.e. labor

Answer 1

Marginal curves exists only in theory that serve as approximations to the real world. Other fields also use such approximations such as treating water as a fluid, when in fact it is composed of individual molecules. There is an entire field of labor economics which examines the implications of the fact that labor is not only discrete, but non identical, and there are hiring costs and added value from experience. How ever most discussions refer to the deviations from the idealized model , so it is necessary to first learn the model, to understand the discussions of the effects of the deviations from it in the real world.

Answer 2

Labor is typically measured in labor hours (each hour of work from a worker is one unit), not the number of persons hired. It is possible to have any fraction of an hour.

Answer 3

yeah, it's discrete.
But when you start talking about thousands of workers, it is easier to use a continuous function.

And there is partial employment like the response above mine says.