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AP Stats
Name________________________
1. What is a statistical inference?
A. A decision, estimate, prediction, or generalization about the population based on
information contained in a sample.
B. A statement made about a sample based on the measurements in that sample.
C. A set of data selected from a larger set of data.
D. A decision, estimate, prediction or generalization about a sample based on
information contained in a population.
E. A set of data that characterizes some phenomenon.
2. Which of the following statements about confidence intervals in INCORRECT?
A. If we keep the sample size fixed, the confidence interval gets wider as we
increase the confidence coefficient.
B. A confidence interval for a mean always contains the sample mean.
C. If we keep the confidence coefficient fixed, the confidence interval gets narrower
as we increase the sample size.
D. If the population std. deviation increases, the confidence interval decreases in
width.
E. If the confidence intervals for two means do not overlap very much, there is
evidence that the two population means are different.
3. You have measured the systolic blood pressure of a random sample of 25 employees of a
company. A 95% confidence interval for the mean systolic blood pressure for the
employees is computed to be (122, 138). Which of the following statements gives a
valid interpretation of this interval?
A. About 95% of the sample of employees have a systolic blood pressure between 122
and 138.
B. About 95% of the employees in the company have a systolic blood pressure
between 122 and 138.
C. If the sampling procedure were repeated many times, that approximately 95% of
the resulting confidence intervals would contain the mean systolic blood pressure
for employees in the company.
D. If the sampling procedure were repeated many times, then approximately 95% of
the sampling means would be between 122 and 138.
E. The probability that the sample mean falls between 122 and 138 is equal to 0.95.
4. The average yield of grain on 9 randomly picked experimental plots of farm was found to
be 150 bushels. If the yield in bushels per plot in previous studies was found to be
approximately normally distributed with a variance of 400 bushels2, a 98%
confidence interval for the mean yield is____.
5. A turkey producer knows from previous experience that profits are maximized by selling
turkeys when their average weight is 12 kg. Before determining whether to put all their
full grown turkeys on the market this month, the producer wishes to estimate their mean
weight. Prior knowledge indicates that turkey weights have a standard deviation of around
1.5 kg. The number of turkeys that must be sampled in order to estimate their true mean
weight to within 0.5 kg with 95% confidence is ____.
6. A statistician selects a random sample of 200 seeds from a large shipment of a certain
variety of tomato seeds and tests the sample for percentage germination. If 155 of the
200 seeds germinate, then a 95% confidence interval for the population proportion of
seeds that germinate is _____.
7. Some scientists believe that a new drug would benefit about half of all people with a
certain blood disorder. To estimate the proportion of patients who would benefit from
taking the drug, the scientists will administer it to a random sample of patient who have
the blood disorder. What sample size is needed so that the 95% confidence interval will
be within 6% of the true proportion.
8. What happens to the confidence interval if
a. the standard deviation is larger
b. the confidence level is increased
9. If the sample size is increased by a factor of 4, the margin of error will
A. increase by a factor of 4
D. decrease by a factor of 2
B. decrease by a factor of 4
E. cannot tell from the given information
C. increase by a factor of 2
10. At Liberty HS a random sample of 20 boys and 25 girls is taken to determine if SAT
math scores differ for the two groups. The 95% confidence interval for the differences
in the mean scores is (-20.57, 35.3). What can you conclude about the scores for boys
and girls at Liberty HS?
11. A recent USA Today survey of 400 people reported that 80% of American adults believe
that teachers should be requir4ed to submit to random drug testing as a condition of
employment. What is the 90% confidence interval? (Show all steps)