问题
单项选择题
An analyst does research about probabilities of a fund and an index. The fund underperforms the index, given the index return is positive is 0.45. The fund underperforms the index and the index return is positive is 0.20. If the two events "the fund underperforms the index" and "the index return is positive" are independent, the probability that the fund underperforms the index or the index return is positive is closest to:（）
A. 0.44
B. 0.69
C. 0.89
答案
参考答案：B
解析：
因为两件事情是独立的，所以“The fund underperforms the index，given the index return is positive”的概率就等于“The fund underperforms the index”的概率，即0.20/0.45=0.44。用加法原则(addition rule of probability)，0.45+0.44-0.20=0.69。