困惑

问题如下：

The current market price of PZ company is $30 per share. Tim has $10,000 to invest including cash $5,000 and $5,000 borrowed from a broker. The maintenance margin is 40%. Which of the following statements is correct?

选项：

A.

A margin call will first occur at $15.

B.

A margin call will first occur at $25.

C.

A margin call will first occur at $20.

解释：

B is correct.

Tim's initial equity is $30×0.5=$15

A margin call will occur when the percentage margin drops to 40%.

We use X to replace the stock price when a margin call will first occur.

So we can solve the following equation

$\frac{\$15+X-\$30}X=40\%$

The solution is X=$25

考点：Leveraged Position

原版书给的计算思路太绕，它其实就是让你计算当股价跌倒多少的时候，会接到保证金催缴电话。根据计算保证金催收电话价格的公式：

initial margin等于50%，因为你自己的自由资金和借来的钱各占一半。MM题目已经给你了是40%，初始股价是30，因此带入计算PL=25。