NO.PZ2018062005000013
问题如下：
There are two projects with the same conventional cash flow patterns and their information listed below:
To make the NPV of two projects equal, the cost of capital should be
选项：
A. smaller than 9%
B. between 9% and 12.06%
C. between 12.06% and 14.78%
解释：
B is correct. The question is more obvious to draw NPV profiles. When cost of capital is 9%, Project B is superior to Project A based on NPV rules (428>255). Due to 14.78%>12.06%, Project A is superior to Project B when cost of capital is larger than 12.06%. Therefore, the crossover rate of Project A and B is between 9% and 12.06%.
小于12.06能理解，为啥大于9还是不清楚。如果两个设联立方程式求解后与9比较要怎么做？