[经济学]lecture 06 consumer theory.ppt

6 The Theory of Consumer Choice 为什么你买东西会犹豫？ 王大妈是个很会过日子的人，买东西精打细算。这天她准备做午饭，看着家里没什么菜了，就去菜市场买菜。她先买了白菜、萝卜和西红柿，花了10元钱；又买了豆腐和粉条，花了5元钱。一看钱包里只剩下2元钱了，本来还想买一斤肉，可钱不够了。这怎么办？不买肉吧，孩子喜欢吃肉，没有肉他又会嚷嚷了。那还得买。王大妈这时才觉得白菜、萝卜和西红柿买多了，于是找卖菜的想退掉一些。买了菜还要退货？真少见。好在卖菜的见王大妈是老主顾，就退了她5元钱的菜。王大妈于是花7元钱买了一斤肉，心满意足的回了家。 The theory of consumer choice addresses the following questions: Do all demand curves slope downward? How do wages affect labor supply? How do interest rates affect household saving? THE BUDGET CONSTRAINT: WHAT THE CONSUMER CAN AFFORD The budget constraint depicts the limit on the consumption “bundles” that a consumer can afford. People consume less than they desire because their spending is constrained, or limited, by their income. THE BUDGET CONSTRAINT: WHAT THE CONSUMER CAN AFFORD The budget constraint shows the various combinations of goods the consumer can afford given his or her income and the prices of the two goods. The Consumer’s Budget Constraint THE BUDGET CONSTRAINT: WHAT THE CONSUMER CAN AFFORD The Consumer’s Budget Constraint Any point on the budget constraint line indicates the consumer’s combination or tradeoff between two goods. For example, if the consumer buys no pizzas, he can afford 500 pints of Pepsi (point B). If he buys no Pepsi, he can afford 100 pizzas (point A). Figure 1 The Consumer’s Budget Constraint THE BUDGET CONSTRAINT: WHAT THE CONSUMER CAN AFFORD The Consumer’s Budget Constraint Alternately, the consumer can buy 50 pizzas and 250 pints of Pepsi. Figure 1 The Consumer’s Budget Constraint THE BUDGET CONSTRAINT: WHAT THE CONSUMER CAN AFFORD The slope of the budget constraint line equals the relative price of the two goods, that is, the price of one good compared to the price of the other. It measures the rate at which the consumer can trade one good for the other. QuickQuiz If a person’s income is $1000 and the price of Pepsi is $5 and the price of pizza is $10, what is the slope of this budget constraint? PREFERENCES: WHAT THE CONSUMER WANTS A consume