Costs are minimized when MPL/w = MPK/r. That is, when marginal product per dollar spent is equal for all inputs. For example, if I can achieve 30 more reports per printer at a cost of $10 per printer hour and only 10 more reports per person at a cost of $10 per person hour, I should increase my use of printers and reduce my use of persons until the benefit:cost ratio for each are equal.
