_______ products are items whose demands are positively related, so that they rise and fall together. An example would be Blu-ray players and Blu-ray discs.

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

Answer: (C)

Complementary products are items that are used together, so their demands tend to move in the same direction. Blu-ray players and Blu-ray discs exemplify this because when more people want players, they also want discs to use with them, and a rise in discs can reinforce demand for players. The idea is that the two goods are jointly consumed, so changes in overall demand or adoption of one product pull the other along with it.

Substitute goods would see demand shift in opposite directions when the price or attractiveness of the other changes, not rise and fall together. Inferior and normal describe how demand responds to income, not how two goods relate to each other.