NO.PZ2015122801000056
问题如下：
Annabelle opened a margin account to buy 450 shares of a public common stock for $31,500, but she didn't have enough money. So she posted initial margin of 30%. The maintenance margin requires 25%. When would Annabelle get a margin call if the stock declined steadily?
选项：
A.
$58.00.
B.
$65.00.
C.
$72.50.
解释：
B is correct.
（1-0.3）/ (1-0.25) *(31500/450)= $65.33
B是正确的。
本题考察的是收到保证金电话对应的公式。
根据上课老师的公式：maintenance margin = 【P1 * initial margin + （P2 – P1）】/P2可得：0.25 = [31500/450 * 0.3 + (P2 – 31500/450)]/P2
P2 = 65.33
利用债务不变原理求解： D=P0*（1-M intital）=PL*(1-MM) PL=Po(1-M intital)/(1-MM) =31500/450(1-30%)/(1-25%) =57.64 我不知道我错在哪里也？
