When an increase in the price of a commodity lead to a fall In the demand for aNOTher, the demand for the two commodities are said to be

Analyze the question: A rise in the price of commodity X causes the demand for another commodity Y to fall. We need the term for this relationship between the two goods.

Explain the concept: There are two main types of related demand:

• Competitive demand (substitutes): Goods that can replace each other, such as Indomie and spaghetti. If the price of one rises, demand for the other rises, because people switch to the cheaper one.
• Joint demand (complements): Goods that are used together, such as car and petrol, or bread and butter. If the price of one rises, demand for it falls, and demand for the other also falls, because they are consumed together.
• Composite demand: One commodity with several uses, such as timber or electricity.
• Derived demand: Demand for a factor of production that comes from the demand for the final product it makes, such as labour or bricks.
• Abnormal demand: Demand that behaves unusually, for example demand that rises when the price rises.

Solution:

1. The price of commodity X rises.
2. The demand for commodity Y falls.
3. Both move in the same direction, so the goods are consumed together (complements).
4. Complementary goods have joint demand.

Check against the other options. Competitive demand would make Y's demand rise, not fall. Composite and derived demand describe other situations entirely.

Answer: E. joint

Tip: Think of "joint" as goods that go together, like a joint account. If one is hit by a price rise, the other suffers too. Remember it this way: Substitutes → opposite direction (competitive). Complements → same direction (joint).