Inputs: Complementary and Substitutable The productivity of an input is the amount of output produced per unit of that input. a Inputs can be complementaryor substitutable this means that a firm's input demands are tightly linked together.9 Inputs: Complementary and Substitutable „ The productivity of an input is the amount of output produced per unit of that input. „ Inputs can be complementary or substitutable. This means that a firm’s input demands are tightly linked together