A complement example would be all except: butter and margarine . When replacing a certain item with with a less costly item is an example of: the substitution effect . An increase in the number of consumers can cause : the demand curve to shift right . when consumers have a need for a product that is urgent : the demand curve is inelastic . Area of economics that deals with behaviors and decision making of units : Microeconomics . A graph showing the quantity demanded : demand curve. The desire, ability and willingness to buy a product : Demand . The extra usefulness of satisfaction a person gets from acquiring of using one or more unit of a product : marginal utility . Products that tend to be used together : complements . Describes very little a change in demand with a large change in price : inelastic . The amount that consumers spend on a product at a particular price: total expenditures . Products that can be used in a place of other products : substitutes . An increase or a decrease in quantity demanded due to a change in the relative price of the replacement product : Substitute effect . Change in quantity demanded due to a change in price that alters a consumers real income : income effect . An increase in demand will shift the demand curve..: Right