Exam (elaborations)

ST 311 Final Exam | Questions and Answers (Complete Solutions)

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ST 311 Final Exam | Questions and Answers (Complete Solutions) A researcher was interested in utilities provided by city governments. The researcher randomly selected 20 counties from a list of all counties in the U.S. From each of these counties the researcher then contacted each city in those c...

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ST 311 Final Exam

A researcher was interested in utilities provided by city governments. The researcher
randomly selected 20 counties from a list of all counties in the U.S. From each of these
counties the researcher then contacted each city in those counties (a total of 192) and
found that 12 (6.25%) of them provided electricity to their residents.

Which of the following are true?
Select all that apply.

-The population of interest is all city governments in the U.S.
-The population of interest is the 192 cities.
-The population of interest is all city governments that provide utilities to their residents.
-The population of interest is 6.25%.
-The parameter of interest is the proportion of the city governments in the U.S. that
provide electricity to their residents.
-The parameter of interest is 6.25%.
-The population of interest is the 20 counties.
-The parameter of interest is the list of all counties in the U.S.

A researcher was interested in utilities provided by city governments. The researcher
randomly selected 20 counties from a list of all counties in the U.S. From each of these
counties the researcher then contacted each city government (a total of 192) and found
that 12 (6.25%) of them provided electricity to their residents. The type of sample used
in this example is a

-simple random sample.
-cluster random sample.
-stratified random sample.
-none of the above.

A professor wanted to determine the proportion of students in his class who have
cheated on an exam. The professor selects a random sample of 30 students from his
class and emails them the question "Have you ever cheated on an exam?". He receives
responses from 10 of the 30 students. Which of the following statements are true?
Select all that apply.

-This study would suffer from undercoverage because the professor should have
selected a sample from the entire student body of the university.
-This study suffers from non-response bias because only 33% of the people surveyed
provided a response.
-This study suffers from response bias since students will not want to tell a professor
whether or not they have cheated.
-The study should not suffer from any bias since it was based on a random sample.

,An instructor in a college class recently gave an exam that was worth a total of 100
points. The instructor inadvertently made the exam harder than he had intended. The
scores were very symmetric, but the average score for his students was 61 and the
standard deviation of the scores was 3 points. The instructor is considering 2 different
strategies for rescaling the exam results:

Method 1:Multiply everyone's score by 1.2.

Method 2:Add 9 points to everyone's score.

Which of the following are true? Select all that apply.

-Method 1 will increase the standard deviation of the students' scores
-Method 1 will decrease the standard deviation of the students' scores.
-Method 2 will decrease the standard deviation of the students' scores.
-Method 2 will increase the standard deviation of the students' scores.

A college professor stops at McDonald's every morning for 10 days to get a number 1
value meal costing $5.39. On the 11th day he orders a number 8 value meal costing
$4.38.

Which of the following are true? Select all that apply.

-During the first 10 days the professor's standard deviation was more than 0.
-During the first 10 days the professor's standard deviation was less than 0.
-During the first 10 days, the professor's standard deviation was 0.
-It is impossible to tell anything about the professor's standard deviation for the first 10
days.
-Considering all 11 days, the professor's standard deviation was lower than the
standard deviation of the first 10 days.
-Considering all 11 days, the professor's standard deviation was higher than the
standard deviation of the first 10 days.
-Considering all 11 days, the professor's standard deviation was the same as the
standard deviation of the first 10 days.
-Considering all 11 days, It is impossible to tell anything about the professor's standard
deviation compared to the first 10 days.

After taking an aptitude test, the computer told Bob that he had a z-score of 1.08.

If scores on the aptitude test are normally distributed, which of the following statements
can Bob conclude from his score?
Select all that apply.

-Bob scored within 2 standard deviations of the mean score.
-Bob did better than the mean score.
-Bob scored within 1 standard deviation of the mean score.

, -Bob did worse than the mean score.
-About 14% of students taking the aptitude test did better than Bob.
-About 14% of students taking the aptitude test did worse than Bob.

The Mental Development Index (MDI) of the Bayley Scales of Infant Development is a
standardized measure used in longitudinal follow-up of high-risk infants. The scores on
the MDI have approximately a normal distribution with a mean of 100 and standard
deviation of 16. What proportion of children have MDI of at least 80?

-0.8944
-0.7881
-0.2119
-0.1056

For a normal distribution, what standard score (Z-score) has 70% of the distribution
above it? Find the closest value listed on the table.

Give your answer to 2 decimal places.
-0.52

Which of the following are NOT likely to be well modeled by a normal distribution
because the distribution is NOT likely to be symmetric? (Hint: Sketch what you think the
histogram would look like based on the information given.)
Select one or more:

-a. The scores from a university's mathematics placement exam in which the minimum
score is 0 and the maximum score is 100. Although there were scores throughout the
entire range, more than half of the students scored over 85.
-b. The number of hours students at a large university work per week at outside jobs.
More than 75% of the students worked less than 10 hours but about 5% had jobs in
which they worked over 30 hours outside the university.
-c. The height (in centimeters) of 10 year old boys in the U.S. Rarely are values lower
than 120 cm or over 160 cm and the majority are between 135 cm and 145 cm.
-d. The amounts of time people wait at a particular bus stop for the bus. About 60% of
the time they wait less than 7 minutes, however, occasionally because of traffic issues
they wait as long as 40 minutes.

A state administered standardized reading exam is given to eighth grade students. The
scores on this exam for all students statewide have a normal distribution with a mean of
517 and a standard deviation of 67. A local Junior High principal has decided to give an
award to any student who scores in the top 10% of statewide scores.

How high should a student score be to win this award?

Give your answer to the nearest integer.
603

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