单选题 There is a 40% chance that the economy will be good next year and a 60% chance that it will be bad. If the economy is good, there is a 50% chance of a bull market, a 30% chance of a normal market, and a 20% chance of a bear market. If the economy is bad, there is a 20% chance of a bull market, a 30% chance of a normal market, and a 50% chance of a bear market. What is the joint probability of a good economy and a bull market?

A、

A. 12%.
B、

B.20%.
C、

C.32%.

【正确答案】 B

【答案解析】Joint probability is the probability that both events, in this case the economy being good and the occurrence of a bull market, happen at the same time. Joint probability is computed by multiplying the individual event probabilities together : (0.40)×(0.50)=0.20 or 20 percent.