STAT 555 DL
Short Test – Workshop Five
Nota:(Habrá un banco de 25 ítems, pero la prueba corta será de solamente 10
preguntas a 2 puntos cada una con un valor total de 20 puntos)
1. Like the normal distribution, the exponential density function f(x)
a. is bell-shaped
b. is symmetrical
c. approaches infinity as x approaches zero
d. approaches zero as x approaches infinity
2.
The mean of the exponential distribution equals the mean of the Poisson
distribution only when the former distribution has a mean that equals
a. 1.0
b. 0.50
c. 0.25
d. any value smaller than 1.0
3. If the random variable X is exponentially distributed, then the mean of X will be
a. greater than the median
b. smaller than the median
c. the same as the median
d. None of the above.
4. Which of the following is not true for an exponential distribution with
parameter  ?
a.   1 / 
b.   1/ 
c. The distribution is completely determined once the value of  is known
d. The distribution is a two-parameter distribution since the mean and
standard deviations are equal
STAT 555 DL
Short Test – Workshop Five
5. If the mean of an exponential distribution is 2, then the value of the parameter
 is:
a. 4
b. 2
c. 1
d. 0.5
6. Which of the following distributions are always symmetrical?
a. Exponential
b. Normal
c. Binomial
d. All continuous distributions are symmetrical.
7. Which of the following is not true for a normal distribution?
a. It is unimodal
b. It is symmetrical
c. It is discrete
d. It has a bell-shape
8. The probability density function f(x) of a random variable x that is normally
distributed is completely determined once the
a. mean and median of x are specified
b. median and mode of x are specified
c. mean and mode of x are specified
d. mean and standard deviation of x are specified
9. A larger standard deviation of a normal distribution indicates that the distribution
becomes
a. narrower and more peaked
b. flatter and wider
c. more skewed to the right
d. more skewed to the left
STAT 555 DL
Short Test – Workshop Five
10. The normal distribution is a:
a. discrete distribution
b. continuous distribution
c. positively skewed distribution
d. none of the above
11. Which of the following are characteristics of the normal distribution?
a. It is a symmetric distribution
b. It is bell-shaped
c. It is asymptotic
d. All of the above
12. Which of the following are correct statements about a normal distribution?
a. It cannot assume negative numbers
b. It is defined by its mean and standard deviation
c. All normal distributions have a variance of at least 1
d. All of the above are correct
13. Which of the following statements is correct regarding the standard normal
distribution?
a. It is called the z-distribution
b. Any normal distribution can be converted to the standard normal
distribution.
c. The mean is 0 and the standard deviation is 1
d. All of the above are correct
14. The area under a normal curve between 0 and -1.75 is
a. .0401
b. .9599
c. .4599
d. none of the above
STAT 555 DL
Short Test – Workshop Five
15. The area under a normal curve less than 1.75 is
a. .0401
b. .9599
c. .4599
d. none of the above
16. A uniform distribution is defined by:
a. its largest and smallest value.
b. largest value.
c. smallest value.
d. none of the above.
17. In the standard normal distribution, what is the probability of finding a z value
between -1.25 and -1.00?
a. 0.3944
b. 0.3413
c. 0.7357
d. 0.0531
18. In its standardized form, the normal distribution:
a. has a mean of 0 and standard deviation of 1.
b. has a mean of 1 and standard deviation of 0.
c. has an area equal to 0.5.
d. cannot be used to approximate discrete probability distribution.
19. Which of the following about the normal distribution is not true?
a. Theoretically, the mean, median and mode are the same.
b. About 2/3 of the observations fall within +1 standard deviation around the
mean.
c. It is a discrete probability distribution.
d. Its parameters are the mean,  x , and standard deviation,  x .
STAT 555 DL
Short Test – Workshop Five
20. If a particular data set were approximately normally distributed, we would find
that approximately:
a. 2 of every 3 observation would between +1 standard deviation around the
mean.
b. 4 of every 5 observations would fall between +1.28 standard deviation
around the mean.
c. 19 of every 20 observations would fall between +2 standard deviation
around the mean.
d. all of the above
21. A standard normal distribution is a normal distribution with
a. a mean of zero and a standard deviation of one
b. a mean of one and a standard deviation of zero
c. a mean usually larger than the standard deviation
d. a mean always larger than the standard deviation
22. If the random variable X is normally distributed with a mean of 75 and a
standard deviation of 8, then P(X>75) is:
a. 0.125
b. 0.500
c. 0.625
d. 0.75
23. Given that Z is a standard normal variable, the variance of Z:
a. is always greater than 2.0
b. is always greater than 1.0
c. is always equal to 1.0
d. cannot assume a specific value
STAT 555 DL
Short Test – Workshop Five
24. Which of the following distributions is suitable to model the length of time that
elapses before the first telephone call is received by a switchboard?
a. exponential
b. normal
c. poisson
d. uniform
25. Which of the following distributions is appropriate to measure the length of time
between arrivals at a grocery checkout counter?
a. uniform distribution
b. normal distribution
c. exponential distribution
d. poisson distribution