Q1. 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 joint probability of a good economy and a bull market?

A)   50%.

B)   20%.

C)   12%.

Q2. What is the probability of a bull market next year?

A)   32%.

B)   20%.

C)   50%.

Q3. For a stock, which of the following is least likely a random variable? Its:

A)   stock symbol.

B)   current ratio.

C)   most recent closing price.

Q4. If two events are mutually exclusive, the probability that they both will occur at the same time is:

A)   0.00.

B)   0.50.

C)   Cannot be determined from the information given.

Q5. Which of the following statements about probability is most accurate?

A)   An outcome is the calculated probability of an event.

B)   A conditional probability is the probability that two or more events will happen concurrently.

C)   An event is a set of one or more possible values of a random variable.

答案和详解如下：

Q1. 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 joint probability of a good economy and a bull market?

A)   50%.

B)   20%.

C)   12%.

Correct answer is B)

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%.

Q2. What is the probability of a bull market next year?

A)   32%.

B)   20%.

C)   50%.

Correct answer is A)

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%.

Q3. For a stock, which of the following is least likely a random variable? Its:

A)   stock symbol.

B)   current ratio.

C)   most recent closing price.

Correct answer is A)

A random variable must be a number. Sometimes there is an obvious method for assigning a number, such as when the random variable is a number itself, like a P/E ratio. A stock symbol of a randomly selected stock could have a number assigned to it like the number of letters in the symbol. The symbol itself cannot be a random variable.

Q4. If two events are mutually exclusive, the probability that they both will occur at the same time is:

A)   0.00.

B)   0.50.

C)   Cannot be determined from the information given.

Correct answer is A)

If two events are mutually exclusive, it is not possible to occur at the same time.  Therefore, the P(A∩B) = 0.

Q5. Which of the following statements about probability is most accurate?

A)   An outcome is the calculated probability of an event.

B)   A conditional probability is the probability that two or more events will happen concurrently.

C)   An event is a set of one or more possible values of a random variable.

Correct answer is C)

Conditional probability is the probability of one event happening given that another event has happened. An outcome is the numerical result associated with a random variable.

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裸考

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[此贴子已经被作者于2009-7-20 11:05:08编辑过]

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