问题如下：
Daisy shorts 1800 shares of KIY company's stock on a 30% initial margin and the broker's lending rate is 2.5%. The current price is $65 per share. The broker charges a commission of $0.02 per share on sales but purchases for free. KIY stock pays an annual dividend of $1 per share. One year later, Daisy buys the 1800 shares at a price of $58 per share and close the position.Which of the following is closest to Daisy's rate of return?
选项：
A.24.98%.
B.24.81%
C.32.55%.
解释：
B is correct.
Initial principal = 1800*65*0.3= 35100. The commission on sale( calculating as a part of initial cost)=1800*0.02=36
Remaining principal=1800*65*0.7=81900 ,so the first expense---lending interest=81900*2.5%=2047.5
The second expense---dividend payment=1*1800=1800, and there is no purchase commission.
The return on this investment=1800*65-1800*58-36-2047.5-1800=8716.5
Yield=8716.5/(35100+36)=24.81%
做完题感觉：这一节课内容上跟实际操作和做题都有很多简化吧。
（1）保证金比例、维持保证金比例没有公式，我为了理解，查完国内融资融券业务，发现国内实务操作公式跟cfa的是相反的系数，国内外是有这个差别吗？我不太懂
（2）既然lending rates出现，我觉得市场上就应该只有broker和short seller，不会出现课程里讲的lender。因为只有券商手里才有票可以出借吧！那课程里面的逻辑图就对不上号，老师讲解还有一个lender，其实他是broker，对不对？
（3） 这里的计算很复杂，是不是应该在课程里补上一道例题呢？要不然这道题很容易出错吧。
