For complement goods, the cross-price elasticity of demand is negative because a price increase in good X causes the quantity demanded of good Y to decrease. For example, computers and software products are complements since one cannot be used without the other. An increase in the price of computers causes a decrease in the quantity demanded for software products. For Substitute goods, the cross-price elasticity of demand is positive since the price increase of good X causes the quantity demanded of good Y to increase. Butter and margarine, tea and coffee, print books and e-books, beef and chicken are all examples of substitute goods.