On the basis of assumptions about the existence of marginal costs to meet the specific needs of the received differential equation costs. It is represented in the form, complying with the requirements of correct writing mathematical expressions with the named values. As a quantitative measure the preferences of the individual entered the coefficients of preferences as a share of costs, respectively, to a high-quality and low-quality goods. Received functions, reflected the dependence of expenditures on interchangeable benefits from the income of the consumer.