This thesis considers an extension of the classical newsboy problems. Demand is assumed to be decreasing with time due to the declining value of its utility. It is also assumed that the supplier has the option to increase (or reduce) the product``s demand by lowering (or raising) its selling price. The objectives considered in this study are maximization of the expected profit and maximization of the probability of achieving a target profit level. The problems are solved with continuous or discrete time approach. The validity of the models is illustrated with example problems.