Demand refers to the entire relationship between the price of goods and the quantity demanded. This relationship is illustrated by the demand curve. The quantity demanded refers to a point on the graph. The willingness and ability to pay curve measures the marginal benefit of a good. When there is a high amount of a good available people are less willing to sacrifice to attain it because it is available in abundance. When there is a small amount of a good available people are more willing to sacrifice to attain it because it is scarce.
When the price of a good rises its opportunity cost rises. Substitutes are goods that can be used in place of a certain good. If a good’s price increases people will buy less of it in favour of buying a substitute for it.
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