A demand curve or a supply curve is a relationship between two, and only two, variables: quantity on the horizontal axis and price on the vertical axis.
2/3 for 1 jar | meaning that: 1 jar: 1 cup (1/3 left) | 1 jar: 1 cup (1/3 left) | 1 jar: 1 cup (1/3 left) | 3/3 are left, and that makes another one (the 4th one).
