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 percent
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
probability of a bull market next year?
【正确答案】
A
【答案解析】Because a good economy and a bad economy are mutually exclusive, the probability of a bull market is the sum of the joint probabilities of (good economy and bull market) and (bad economy and bull market) : (0.40) × (0.50) + (0.60) × (0.20) =0.32 or 32 percent.