曼昆经济学原理的题目急要哎P24第五题P41第二题P68第五题P89第四题P158第十一题

第一,不考虑500万是因为500是沉淀成本,也就是已经不可能收回来的成本,在进行第二次投资选择的时候已经不能影响决策,因为不管你之前投资了1元钱还是1亿元,追加投资的时候只能考虑追加投资的收益和成本.第二,在第二次追加投资时,你面临的选择是你愿意投入多少换回来这300万,所以即便你追加投资299.999万,你也能多赚回来1块钱,企业家的目的是利润最大化,或者成本最小化,你能赚回来一块钱就少赔一块钱,所以为了把预期的300万赚回来,他的最大追加投资会无限趋近于300万,极限就是300万了.

英文版的案例,不明白的话直接用google翻译把英文翻译成中文.
PRINCIPLE #3:RATIONAL PEOPLE THINK AT THE MARGIN
Decisions in life are rarely black and white but usually involve shades of gray.
When it’s time for dinner,the decision you face is not between fasting or eating
like a pig,but whether to take that extra spoonful of mashed potatoes.When exams
roll around,your decision is not between blowing them off or studying 24
hours a day,but whether to spend an extra hour reviewing your notes instead of
watching TV.Economists use the term marginal changes to describe small incremental
adjustments to an existing plan of action.Keep in mind that “margin”
means “edge,” so marginal changes are adjustments around the edges of what you
are doing.
In many situations,people make the best decisions by thinking at the margin.
Suppose,for instance,that you asked a friend for advice about how many years to
stay in school.If he were to compare for you the lifestyle of a person with a Ph.D.
to that of a grade school dropout,you might complain that this comparison is not
helpful for your decision.You have some education already and most likely are
deciding whether to spend an extra year or two in school.To make this decision,
you need to know the additional benefits that an extra year in school would offer
(higher wages throughout life and the sheer joy of learning) and the additional
costs that you would incur (tuition and the forgone wages while you’re in school).
By comparing these marginal benefits and marginal costs,you can evaluate whether
the extra year is worthwhile.
As another example,consider an airline deciding how much to charge passengers
who fly standby.Suppose that flying a 200-seat plane across the country costs
the airline $100,000.In this case,the average cost of each seat is $100,000/200,
which is $500.One might be tempted to conclude that the airline should never
sell a ticket for less than $500.In fact,however,the airline can raise its profits by
thinking at the margin.Imagine that a plane is about to take off with ten empty
seats,and a standby passenger is waiting at the gate willing to pay $300 for a seat.
Should the airline sell it to him?Of course it should.If the plane has empty seats,
the cost of adding one more passenger is minuscule.Although the average cost of
flying a passenger is $500,the marginal cost is merely the cost of the bag of peanuts
and can of soda that the extra passenger will consume.As long as the standby passenger
pays more than the marginal cost,selling him a ticket is profitable.
As these examples show,individuals and firms can make better decisions by
thinking at the margin.A rational decisionmaker takes an action if and only if the
marginal benefit of the action exceeds the marginal cost.

问题1：市场均衡时的价格代表了完成交易的消费者中对该商品的最低评价,也代表了厂商在均衡产量下生产最后一单位的边际成本.事实上你可以将供求达到均衡看作一个消费者和厂商相互谈判出价的过程,厂商会首先将产品卖给评价最高的消费者,而消费者会首先选择生产成本最低（也即可以卖出最低价格）的厂商.考虑到生产的边际成本递增和消费者评价逐渐降低,市场将最终达到一个稳定状态,即最后一个完成交易的消费者对商品的评价恰好等于厂商售出这最后一单位产品的边际成本,这就达到了均衡,产生了均衡价格.所以在均衡价格下,除了最后一个消费者和生产者外,其他完成交易的消费者和生产者都有剩余,总剩余不为0.

问题2：如问题1所述,总剩余最大化只是表示在这个市场中所有可能进行的交易所达到的剩余总和最大,不管买者评价和卖者成本如何,只要最高的消费者评价不低于最低的卖者成本,均衡总能达到.

问题3：数量大于均衡数量时,你可以在供求两条线之间画出四个直角三角形,即作出斜向上的供给线、斜向下的需求线、水平的均衡价格线和竖直的数量线（是完成交易的数量,不是均衡数量）.消费者剩余等于左上方的三角形面积减去右下方的三角形面积,生产者剩余等于左下方的三角形面积减去右上方的三角形面积,那么总剩余就是左侧两个三角形面积和减去右侧两个三角形面积和.之所以要减去右边是因为超过均衡数量的部分,消费者和生产者的剩余都是负的.

个人觉得图上面的的分析不是很恰当.
首先,这道题中人们由于决定多生孩子,那么势必导致家用旅行车的需求增多,及时存在因为预期而减少的需求,但总的需求还是增加的,那么需求曲线右移,导致价格上升.
在这里理性预期并不是影响需求和供给的最重要的因素,看上面也说了需求和供给的预期因素都受到影响,一个使得需求适量减少,一个使得供给减少,我们可以理解为预期的作用相互抵消,但是最根本的影响因素,是人们多生孩子导致的总的需求的增多,这不是一些小小的预期因素就能干扰的.

pizza供给不变,需求变低,价格和需求量都下降.啤酒价格的变动只会影响买者的决定,但是不会影响生产pizza的厂家的决定,所以pizza供给不会变动.pizza价格只会让供给量沿着供给曲线变动,不会使供给曲线整个移动.注意：供应和供应量是两个不同的概念,影响他们的因素也不一样,这两个容易混.

1.等待退票的人是什么人呢?当然是想做飞机而没有买到票的人.教材的意思是说有一个空位,则飞一次每个空位就会损失500美元,10个则是5000美元.航空公司将票价降低,把10个座位填满,就可以另损失降到最低.最低能降到多低呢?只要降价票价格比每个乘客的编辑成本要高,航空公司就划算.
票价应不低于500美元这句的前提是每次飞行都能满员.但实际常常不能满员,可航空公司不能因为某一次飞行不能满员就取消该次航班.所以航空公司要考虑如何在不满员或这说是赔钱的情况下如何降低损失.比如说把票价降低到300美元来招揽更多顾客.
2.有利可图是指和有10个空位的不满员情况比较.赔2000美元相对于赔5000美元来讲就叫有利可图了.