Gyros and french fries are complementary goods because people like to consume them together. When the price of french fries decreases, it becomes less costly to consume french fries and gyros together. Therefore, people increase their consumption of gyros at any given price. Consequently, the demand for gyros increases, and the demand curve shifts to the right. Notice that it is the price of french fries, rather than the quantity demanded of french fries, that changes the demand for gyros.
Note that the supply curve does not shift because none of the factors affecting supply have changed. In particular, the supply curve shifts in response to changes in the following:
• | Price of inputs |
• | Production technology |
• | Number of producers |
• | Expectations of producers |