The marginal product of labor MPL is the change in output resulting from a 1-unit change in labor input,or AQ/AL. As a result, MC=△VC/△Q=w△L/△Q=wMPL Copyright by CaidonghongCopyright by Caidonghong The marginal product of labor MPL is the change in output resulting from a 1-unit change in labor input, or △Q/△L. As a result, MC = △VC/△Q = w△L/△Q = w/MPL