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 of Butter $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.