A product's demand relationship with another product that rises and falls together is called what in this material?

• A. Complementary
• B. Substitute
• C. Inferior
• D. Normal

Answer: (A)

Two goods are complementary when they are typically used together, so the demand for one tends to align with the demand for its partner. When more people want the paired item, they also buy more of the other, and when interest in the pair wanes, both see reduced demand. A classic example is coffee and creamer: as coffee purchases rise, creamer purchases tend to rise as well because people usually consume them together. This explains why their demand movements occur in tandem. Substitutes would instead move in opposite directions—if one becomes more desirable, the other usually declines. Inferior and normal describe how demand shifts with income, not how two different products’ demands relate to each other.