STT 231 PRACTICE EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026
The type of aircraft - Answers Categorical
The flight number (e.g., Flight 1013). - Answers Categorical
The number of passengers. - Answers Quantitative
Whether the flight departed and arrived on schedule. - Answers Categorical
The number of luggage each passenger checks for flight - Answers Not a variable with respect to
these observational units
Aspirin and Cancer~ Aspirin, the medicine commonly used for headache and fever, has been shown to
reduce the risk of stroke and heart attack in susceptible people. Observational studies have suggested
that aspirin may also reduce the risk of cancer. 500 volunteer women participated in a carefully
designed experimental study to test the role of aspirin on reducing the risk of cancer The table below
summarizes some of the study results. Use these results to answer the following questions.
Which of the following terms applies to the variable 'cancer status' in this study? Circle all that apply -
Answers categorical and response
Among those participants that used aspirin, what is the probability of getting cancer? (You may leave
your answer as a fraction.) - Answers 30/250
What is the probability that a randomly selected participant took aspirin and got cancer? (You may
leave your answer as a fraction.) - Answers 30/500
Consider the mosaic plot to the right, which summarizes the study results. Are the events 'took
aspirin' and 'get cancer' independent? Clearly circle 'yes' or 'no' and provide a brief written support. -
Answers Yes. the proportion of observations in the aspirin group who got cancer is almost identical to
the proportion in the " no cancer" group
Consider the following graph, which displays the distribution of text messages sent in the last hour by
a sample of 10students enrolled in a large introductory statistics course. The mean of this distribution
is 𝑥̅ = 11.0 text messages, the median is 𝑥̃ = 9.5 text messages, and the standard deviation is 𝑠 = 6 text
messages. - Answers The mean, median, and standard deviation all increase. Draw this data point on
the graph above and label it (A).
The mean, median, and standard deviation all decrease. Draw this data point on the graph above and
label it (B)
Hospital stays ~ A survey of the population of over four hundred short stay hospitals in the US was
conducted in 1976.To get a sense of the mean number of patients discharged from the hospitals
during January 1968, a researcher chose32 hospitals at random from all the the short stay hospitals ,
and used the mean 𝑋 ̅ = the mean number of patients discharge across the 32 hospitals as an estimate
of the 𝜇 = mean number of patients discharged across the more than400 short stay hospitals in the
US.
The standard error of 𝑋 ̅ from this researcher's sample of 𝑛 = 32 is approximately 100. Which of the
following statements correctly interprets this value in the context of estimating the true mean
number of patients discharged from the population of short stay hospitals in the US during January
1968? - Answers The average distance between any given 𝑋 ̅ and the parameter they estimate, 𝜇, is
approximately 100.
To the right is a histogram of the sampling distribution of 𝑋 ̅ . Use this histogram to decide whether the
italicized statement below is true or false
It is more likely to randomly sample 32 hospitals and witness 𝑋 ̅ >900 than it is to witness 𝑋 ̅ < 600? -
Answers True
Another researcher plans to choose 64 hospitals at random from the list of all hospitals, and to use
the mean number of patients discharged of these 64 hospitals as an estimate of the mean number of
patients discharged from the population. What features of the sampling distribution for this
researcher's estimator would you expect to be similar to the sampling distribution based on 32
hospitals? What features would you expect to be different? - Answers we should expect the standard
deviation of the sampling distribution (standard error) to be smaller at larger sample sizes, so the
sampling distribution of means computed for sample size n=64 should display less variability than the
The type of aircraft - Answers Categorical
The flight number (e.g., Flight 1013). - Answers Categorical
The number of passengers. - Answers Quantitative
Whether the flight departed and arrived on schedule. - Answers Categorical
The number of luggage each passenger checks for flight - Answers Not a variable with respect to
these observational units
Aspirin and Cancer~ Aspirin, the medicine commonly used for headache and fever, has been shown to
reduce the risk of stroke and heart attack in susceptible people. Observational studies have suggested
that aspirin may also reduce the risk of cancer. 500 volunteer women participated in a carefully
designed experimental study to test the role of aspirin on reducing the risk of cancer The table below
summarizes some of the study results. Use these results to answer the following questions.
Which of the following terms applies to the variable 'cancer status' in this study? Circle all that apply -
Answers categorical and response
Among those participants that used aspirin, what is the probability of getting cancer? (You may leave
your answer as a fraction.) - Answers 30/250
What is the probability that a randomly selected participant took aspirin and got cancer? (You may
leave your answer as a fraction.) - Answers 30/500
Consider the mosaic plot to the right, which summarizes the study results. Are the events 'took
aspirin' and 'get cancer' independent? Clearly circle 'yes' or 'no' and provide a brief written support. -
Answers Yes. the proportion of observations in the aspirin group who got cancer is almost identical to
the proportion in the " no cancer" group
Consider the following graph, which displays the distribution of text messages sent in the last hour by
a sample of 10students enrolled in a large introductory statistics course. The mean of this distribution
is 𝑥̅ = 11.0 text messages, the median is 𝑥̃ = 9.5 text messages, and the standard deviation is 𝑠 = 6 text
messages. - Answers The mean, median, and standard deviation all increase. Draw this data point on
the graph above and label it (A).
The mean, median, and standard deviation all decrease. Draw this data point on the graph above and
label it (B)
Hospital stays ~ A survey of the population of over four hundred short stay hospitals in the US was
conducted in 1976.To get a sense of the mean number of patients discharged from the hospitals
during January 1968, a researcher chose32 hospitals at random from all the the short stay hospitals ,
and used the mean 𝑋 ̅ = the mean number of patients discharge across the 32 hospitals as an estimate
of the 𝜇 = mean number of patients discharged across the more than400 short stay hospitals in the
US.
The standard error of 𝑋 ̅ from this researcher's sample of 𝑛 = 32 is approximately 100. Which of the
following statements correctly interprets this value in the context of estimating the true mean
number of patients discharged from the population of short stay hospitals in the US during January
1968? - Answers The average distance between any given 𝑋 ̅ and the parameter they estimate, 𝜇, is
approximately 100.
To the right is a histogram of the sampling distribution of 𝑋 ̅ . Use this histogram to decide whether the
italicized statement below is true or false
It is more likely to randomly sample 32 hospitals and witness 𝑋 ̅ >900 than it is to witness 𝑋 ̅ < 600? -
Answers True
Another researcher plans to choose 64 hospitals at random from the list of all hospitals, and to use
the mean number of patients discharged of these 64 hospitals as an estimate of the mean number of
patients discharged from the population. What features of the sampling distribution for this
researcher's estimator would you expect to be similar to the sampling distribution based on 32
hospitals? What features would you expect to be different? - Answers we should expect the standard
deviation of the sampling distribution (standard error) to be smaller at larger sample sizes, so the
sampling distribution of means computed for sample size n=64 should display less variability than the
