Consider some consumer's demand for used movie videotapes, shown to the right. When these tapes sell for $5 she purchases 4. The willingness to pay for the 4th movie is 5, the same as the price. Any utility maximizing consumer with this demand curve would make the same purchase decision.

    For the first through third movies purchased, her willingness to pay was above $5, but she paid $5 for each tape. This additional willingness to pay, above the market price, is consumer surplus. On the graph to the right the area of consumer surplus is green, while total expenditure is red. Total willingness to pay for 4 videos is the green + red areas, or the entire area under the demand curve to the left of the quantity consumed.

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