There is a 50 percent chance that the Fed

问题单项选择题

There is a 50 percent chance that the Fed will cut interest rates tomorrow. On any given day, there is a 67 percent chance the DJIA will increase. On days the Fed cuts interest rates, the probability the DJIA will go up is 90 percent. What is the probability that tomorrow the Fed will cut interest rates or the DJIA will go up（）

A. 1.00.

B. 0.72.

C. 0.33.

答案

参考答案：B

解析：

This requires the addition formula. From the information: P(cut interest rates)=0.50 and P (DJIA increase)=0.67, P(DJIA increase | cut interest rates)=0.90. The joint probability is 0.50×0.90=0.45. Thus P (cut interest rates or DJIA increase)=0.50+0.67-0.45=0.72.