How butter's price shifts demand for a substitute and a complement One price change, opposite demand shifts Drag butter's current-price point up or down. Butter Weekly pounds of butter demanded Price per pound $4.00 4.0 Margarine substitute Weekly pounds of margarine demanded Price per pound $4.00 4.0 Dinner rolls complement Dozens of dinner rolls demanded per week Price per dozen $4.00 4.0 Butter: $4.00 per pound; 4.0 pounds demanded per week. At butter's normal price, both related-good demand curves are unchanged.