Assignment 9
Due date: 11/14/08
1. Suppose that a random sample of 50 bottles of a particular brand of cough medicine is
selected and the alcohol content of each bottle is determined. Let μ denote the true
average alcohol content for the population of all bottles of the brand under study. If the
sample of 50 results in a 95% confidence interval for μ of (7:8; 9:4), which of the
following statements is correct?
A. There is a 95% chance that the true mean alcohol content, μ, of this brand falls
between
7.8 and 9.4.
B. The estimate, , is within 95% of the true mean, μ.
C. If the process of selecting a sample of size 50 and then computing the corresponding
95% confidence interval is repeated many times, approximately 95% of the resulting
intervals will include μ..
D. If the process of selecting a sample of size 50 and then computing the corresponding
95% confidence interval is repeated many times, approximately 95% of the resulting
intervals will fall within (7:8; 9:4).
.
2. Which of the following does NOT affect the width of a confidence interval for
the mean of a normal population when σ is known?
A. the population standard deviation
B. the sample standard deviation
C. the sample size
D. the confidence level
3. Suppose a 90% confidence interval for the true proportion of A&M students who
watch Walker: Texas Ranger is (0.22, 0.53), and a 90% confidence interval for the true
proportion of t.u. students who watch is (0.29, 0.42). From this we can conclude
A. more Aggies watch than t.u. students.
B. less Aggies watch than t.u. students.
C. it's plausible that the same proportion from either school watch.
D. we have more confidence that the A&M interval contains the true proportion since it is
wider than the other.
Text-book Problem
6.19, 6.20, 6.32, 6.34
