[2008] Topic 3: Review of Statistics I: Probability and Probability Distribut

aianjie

 

AIM 1: Define random variables, and distinguish between continuous and discrete random variables.

1、Which of the following statements about probability is most accurate?

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

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

C) Out of a sample of 100 widgets 10 were found to be defective, 20 were perfect, and 70 were OK. The probability of picking a perfect widget at random is 29%.

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

veig0900

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aianjie

 

2、A company says that whether its earnings increase depends on whether it increased its dividends. From this we know:

A) P(both dividend increase and earnings increase) = P(dividend increase).  

B) P(earnings increase | dividend increase) is not equal to P(earnings increase). 

C) P(dividend increase or earnings increase) = P(both dividend and earnings increase). 

D) P(dividend increase | earnings increase) is not equal to P(earnings increase). 

aianjie

 

The correct answer is B

If two events A and B are dependent, then the conditional probabilities of P(A|B) and P(B|A) will not equal their respective unconditional probabilities (of P(A) and P(B), respectively). The other choices may or may not occur, e.g., P(A | B) = P(B) is possible but not necessary.

aianjie

   

3、If the outcome of event A is not affected by event B, then events A and B are said to be:

A) mutually exclusive.

B) statistically independent.

C) collectively exhaustive.

D) conditionally dependent.

 

aianjie

 

The correct answer is B

If the outcome of one event does not influence the outcome of another, then the events are independent.

aianjie

 

The correct answer is D

This is the definition of a multivariate distribution.