Statistics 211 Practice Exam 2
Answer key
1. The formula E(X) = np
can be used to find the expected value of
a. any numeric random variable
b. only Poisson random variables
c. only normal random variables
d. only binomial random variables
*
e. none of the above
2. For a specific sample size, the width of a 95% confidence interval on
μ
a. would be larger than the width of a 90% confidence interval on
μ
. *
b. would be smaller than the width of a 90% confidence interval on
μ
.
c. would be the same as the width of a
90% confidence interval on
μ
.
d. cannot be compared to the width of a 90% confidence interval on
μ
.
e. none of the above
3. A random sample of 400 WVU students was selected, in which 150 students stated that
they had used “ an illegal drug”. A 95 % confidence interval on binomial parameter p
goes from 33.5% to 41.5%.
Which of the following statements provides the appropriate
interpretation of this 95 % confidence interval?
a. 95% of all WVU students use an illegal drug between 33.5% and 41.5% of the
time.
b. There is a 95% probability that a randomly selected WVU student has used an
illegal drug.
c. We are 95% confident that between 33.5% and 41.5% of all WVU students
have used an illegal drug. *
d. We are 95% confident that between 33.5% and 41.5% of the sample of 400
WVU students have used an illegal drug.
e. none of the above
4. The standard normal distribution is a normal distribution whose
a. mean is
μ
=1 and standard deviation
σ
=0
b. mean is
μ
=0 and standard deviation
σ
=1 *
c. mean
μ
can have any real value and standard deviation
σ
=1
d. mean
μ
can be determined by using a z-score
e. none of the above
5. A radar gun is used to measure the speed of 74 randomly selected automobiles on
Interstate 79, and the data is used to construct a 95% confidence interval on the mean

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*Sign up*speed of all automobiles on I-79. The 95 % confidence interval goes from 64.4 mph to
71.6 mph. Which of the following statements provides the appropriate interpretation of
this 95 % confidence interval?
a. 95% of all automobiles on I-79 travel between 64.4 mph and 71.6mph.
b. There is a 95% probability that the mean speed of all automobiles on I-79 is
between 64.4 mph and 71.6 mph.
c. We are 95% confident that the mean speed of all automobiles on I-79 is

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