X is a discrete random variable that can have values from 0 to infinity, and occurrences of the events X counts are independent. The standard deviation of X is equal to the square root of the mean. The probability distribution of X is a(n) （）distribution.

单项选择题The empirical rule tells us that approximately of the values cluster within a distance of 1 standard deviation from the mean for a bell-shaped distribution（）

A.68%
B.95%
C.99.7%
D.none of the above

单项选择题The reason that we prefer the sample standard deviation as our measure of typical variation instead of the sample variance is that（）

A.the variance is not as accurate a measurement as the standard deviation
B.the standard deviation has been corrected for bias while the variance has not
C.the standard deviation is in the same units as the data values.
D.the variance is in the same units as the data values.

单项选择题The sum of the deviations may be 0.00.To get around this problem，we use the（）of the deviations

A.square
B.absolute value
C.minimum
D.maximum

单项选择题deviation is the distance between a（）and the（）.（）

A.median；mean
B.data point；mean
C.quartile；median
D.data point；median

单项选择题A theorem that allows us to use thenormal probability distribution to approximate the sampling distribution of sample means and sample proportions whenever the sample size is large is known as the（）

A.approximation theorem
B.normal probability theorem
C.central limit theorem
D.central normality theorem

单项选择题The purpose of statistical inference is to provide information about the（）

A.sample based upon information contained in the population
B.population based upon information contained in the sample
C.population based upon information contained in the population
D.mean of the sample based upon the mean of the population

单项选择题If A and B are independent events，then（）

A.P（A） must be equal to P（B）
B.P（A） must be greater thanP（B）
C.P（A） must be less than P（B）
D.P（A） must be equal to P（A│B）

单项选择题Exhibit 2 The following represents the probability distribution for the daily demand of computers at a local store. Refer to Exhibit 2.The probability of having a demand for at least two computers is（）

A.0.7
B.0.3
C.0.4
D.1.0

单项选择题The student body of a large university consists of 60%female students.A random sample of 8 students is selected.What is the probability that among the students in the sample exactly two are female？（）

A.0.0896
B.0.2936
C.0.0413
D.0.0007

单项选择题A weighted average of the value of a random variable, where the probability function provides weights is known as（）

A.a probability function
B.a random variable
C.thee xpected value
D.random function