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1、北京大学国家发展研究院2014年秋季学期 本科双学位课程 中级微观经济学(2班) 第六讲： 购买和销售 任课教师：李力行 第9章 购买和销售 Endowments （禀赋）禀赋） Budget constraints with endowments Net demands - Price offer curve Example: Labor supply - Comparative statics Slutsky equation revisited Buying and Selling How is income generated? When something is bought som
2、ething else must be sold. What will be bought? What will be sold? Who will be a buyer? Who will be a seller? How does the value of income depend upon commodity prices? Endowments The list of resource with which a consumer starts is his endowment. A consumers endowment will be denoted by the vector .
3、 E.g. states that the consumer is endowed with 10 units of good 1 and 2 units of good 2. What is the endowments value? For which consumption bundles may it be exchanged? (,)(,) 12 10 2 Endowments p1=2 and p2=3 so the value of the endowment is Q: For which consumption bundles may the endowment be exc
4、hanged? A: For any bundle costing no more than the endowments value. (,)(, ) 12 10 2 pp 1122 2103226 Budget Constraints Revisited So, given p1 and p2, the budget constraint for a consumer with an endowment is The budget set is (,) 12 p xp xpp 11221122 . (,), ,. xxp xp xpp xx 121 12 21122 12 00 Budge
5、t Constraints Revisited x2 x1 1 1 2 2 p xp xpp 11221122 Budget set (,), , xxp xp xpp xx 121 12 21122 12 00 Budget Constraints Revisited x2 x1 1 1 2 2 p xp xpp 11221122 p xp xpp 1 1221122 Budget set Budget Constraints Revisited x2 x1 1 1 2 2 p xp xpp 11221122 The endowment point is always on the budg
6、et constraint. p xp xpp 1 1221122 So price changes pivot the constraint around the endowment point. Budget Constraints Revisited The constraint is That is, the sum of the values of a consumers net demand is zero. pxpx 111222 0()(). p xp xpp 11221122 Net Demands Suppose and p1=2, p2=3. Then the const
7、raint is If the consumer demands (x1*,x2*) = (7,4), then 3 units of good 1 exchange for 2 units of good 2. Net demands are x1*- 1 = 7-10 = -3 and x2*- 2 = 4 - 2 = +2. (,)(, ) 12 10 2 p xp xpp 11221122 26 . Net Demands p1=2, p2=3, x1*- 1 = -3 and x2*- 2 = +2 so pxpx 111222 23320 ()() (). The purchase
8、 of 2 extra units of good 2 at $3 each is funded by giving up 3 units of good 1 at $2 each. Net Demands x2 x1 1 1 2 2 pxpx 111222 0()() x2* x1* At prices (p1,p2) the consumer sells units of good 1 to acquire more units of good 2. Net Demands x2 x1 1 1 2 2 p xp xpp 1 1221122 x2* x1* At prices (p1,p2)
9、 the consumer sells units of good 2 to acquire more of good 1. Net Demands x2 x1 pxpx 111222 0()() x2*= 2 2 x1*= 1 1 At prices (p1”,p2”) the consumer consumes her endowment; net demands are all zero. p xp xpp 11221122 Net Demands x2 x1 1 1 2 2 pxpx 111222 0()() Price-offer curve contains all the uti
10、lity-maximizing gross demands for which the endowment can be exchanged. Net Demands x2 x1 1 1 2 2 pxpx 111222 0()() Price-offer curve Sell good 1, buy good 2 Net Demands x2 x1 1 1 2 2 pxpx 111222 0()() Price-offer curve Buy good 1, sell good 2 19 20 21 Some Results about Price Change If a consumer i
11、s a net seller of a good, when the price of that good decreases, if she remains a seller then the consumer is worse off. However, if she switches to a net buyer, then she may be better off. If a consumer is a net buyer of a good, when the price decreases, the consumer will remain a buyer and be bett
12、er off. 22 A net seller facing falling price 23 A net buyer facing falling price Labor Supply A workers non-labor income endowment is m, and time endowment is R hours of time, which can be used for labor or leisure. = (R,m). Consumption good C, price is pc. w is the wage rate. Labor Supply The worke
13、rs budget constraint is pcC = wL + m where C, R denote gross demands for the consumption good and for leisure. p Cw RRm c () p Cw Rw Rm c endowment value expenditure Labor Supply p Cw RRm c () rearranges to C w p R mwR p cc . Labor Supply C R R endowment C w p R mwR p cc mwR pc slope = , the real wage rate w pc m/pc Labor Supply C R R endowment C w p R mwR p cc mwR pc C* R* leisure demanded labor supplied m/pc Slutsk
