Suppose our consumer realized that she was purchasing too much and cut back to buying only 4 CDs when the price is 10, in order to maximize her utility. Would this work?

    If, when the price is 10, she buys only 4 CDs then every one she buys is "worth it," in the sense that her marginal willingness to pay is always above the price. Nevertheless, she's still worse off than if she were to buy 7. The total cost to her of buying the 5th, 6th and 7th CDs is equal to the orange area to the right. The added utility she would gain is equal to the orange + green areas, so she is worse off by an amount equal to the green area by only buying 4 and not 7 CDs. (We will learn later that this green area is consumer surplus for the 5th-7th CDs, but don't worry about this now).

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