咱想要详细的过程，因为是要交的
大家别怪咱这样作弊，实在因为老师用英文上课听不懂，而上课的都是大三的师兄师姐，他们都是学过高级微观课的，老师都讲给他们听啊，我刚过完大一，悔只在我选错课...
大家麻烦下...
拜托了，学分绩啊~~~~

Suppose there are two types of college students: A (able) and C (challenged).
You, a potential employer, are willing to pay $150,000 a year to a
type A, and $100,000 to a type C (you have to pay this much in a competitive
job market). You cannot directly observe any particular job applicant’s
type. But you know that types differ in their tolerance for taking a tough
course rather than an easy one in college. Suppose that the A types regard
the cost of each tough course as equivalent to $6,000 a year of salary, while
the C types regard it as $9,000 a year of salary.
a) Find first the minimum number of tough courses so that anyone who
has taken that number of tough courses will be regarded as a type A, and
anyone who has taken less than that number will be regarded as a type C.
Then write down your wage function.
b) If the populations of these two types are 50-50, show that both types
are better off under pooling in which you pay all the same salary.

以上不方便看的话，下面链接的图片“未命名.bmp“是原文（PDF）的截图，或者用纳米盘链接下载：http://d.namipan.com/d/b07aa77b32c5e0a91eeab686c50e0a8db529e926e6701b00

再次拜谢~~

咱第一次发悬赏，也不知道这题值多少~大家嫌少跟咱说咱可以提高悬赏~^_^