问题
单项选择题
The manager of a pension fund determines that during the past five years 85 percent of the stocks in the portfolio have paid a dividend and 40 percent of the stocks have announced a stock split. If 95 percent of the stocks have paid a dividend or announced a stock split, the joint probability of a stock paying a dividend and announcing a stock split is closest to:()
A. 30%.
B. 45%.
C. 55%.
答案
参考答案:A
解析:
[分析]: 令支付股息的事件为A,宣布拆股的事件为B,则有: P(A或B)=P(A)+P(B)-P(AB) 进一步地,可得: P(AB)=P(A)+P(B)-P(A或B)=0.85+0.4-0.95=0.3 [考点] 与联合概率有关的计算