Question

If the demand for good Y decreases as the price of another good rises, how are the two goods related?

Answer 1

If the demand for good Y decreases as the price of another good rises, then the two goods are complementary goods. Complementary goods are goods that are used together (e.g., tea and sugar, petrol and cars). When the price of one good increases, its demand falls, and since the other good is used with it, its demand also falls.