标题: Reading 8: Probability Concepts-LOS a 习题精选 [打印本页]
作者: 1215 时间: 2011-3-1 15:04 标题: [2011]Session 2-Reading 8: Probability Concepts-LOS a 习题精选
Session 2: Quantitative Methods: Basic Concepts
Reading 8: Probability Concepts
LOS a: Define a random variable, an outcome, an event, mutually exclusive events, and exhaustive events.
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?
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%.
What is the probability of a bull market next year?
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%.
作者: 1215 时间: 2011-3-1 15:04
For a stock, which of the following is least likely a random variable? Its:
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C) |
most recent closing price. | |
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.
作者: 1215 时间: 2011-3-1 15:04
If two events are mutually exclusive, the probability that they both will occur at the same time is:
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B) |
Cannot be determined from the information given. | |
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If two events are mutually exclusive, it is not possible to occur at the same time. Therefore, the P(A∩B) = 0.
作者: 1215 时间: 2011-3-1 15:05
Which of the following statements about probability is most accurate?
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An outcome is the calculated probability of an event. | |
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An event is a set of one or more possible values of a random variable. | |
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A conditional probability is the probability that two or more events will happen concurrently. | |
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.
作者: 1215 时间: 2011-3-1 15:05
If event A and event B cannot occur simultaneously, then events A and B are said to be:
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statistically independent. | |
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collectively exhaustive. | |
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If two events cannot occur together, the events are mutually exclusive. A good example is a coin flip: heads AND tails cannot occur on the same flip.
作者: 1215 时间: 2011-3-1 15:05
In any given year, the chance of a good year is 40%, an average year is 35%, and the chance of a bad year is 25%. What is the probability of having two good years in a row?
The joint probability of independent events is obtained by multiplying the probabilities of the individual events together: (0.40) × (0.40) = 0.16 or 16%.
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