AP Statistics
Wkst- One Population Proportion CI
Name:____________________________________
Date:_____________________________________
1. A computer company is interested in investigating the proportion of families who own computer in a large
city. The management department conducted a survey by randomly select 400 families from the city and found
that 260 owned at least one computer.
(a) From this sample, what will you estimate the proportion of families in the city who own at least one
computer?
(b) What is the margin of error using the above sample proportion to estimate the true proportion?
(c) From this sample, can you find a 95% confidence interval for population proportion of families in this city
who own at least one computer?
(d) How can you interpret the result found in (b)?
(e) What will be the 99% confidence interval of the population proportion of families in the city who own at
least one computer?
2. In recent years, buying merchandise on Internet is a hot issue. An Internet virtual store in interested in
investigating the proportion of individuals who visited similar sites will actually buy merchandise on line. A
study is conducted for this purpose. The buying activities of randomly selected 1000 visitors are recorded. It
shows that 125 of them actually buying merchandise on line.
(a) What is the estimate of the true proportion of visitors who purchase on line?
(b) What is the margin of error using the above sample proportion to estimate the true proportion?
(c) With 90% of confidence, what is your estimated interval of the true proportion?
(d) Find a 97% confidence interval for the true proportion.
3. After the September 11th, Bush has gains a great deal of support for his handling of the tragedy. A poll of
1000 USA citizens were surveyed. The approval rate of Bush’s handling of the national tragedy was86%.
(a) What is the margin of error for this survey?
(b) Can you obtain a 90% confidence interval of the true population proportion of USA citizens who
approve Bush’s handling of the tragedy?
(c) Can you obtain a 95% confidence interval of the true population proportion of USA citizens who
approve Bush’s handling of the tragedy?
(d) If a poll surveyed 2000 USA citizens and find the same proportion as the above 1000 citizens, what is
the margin of error for this survey?
(e) If USA Today would like to conduct a poll to find out the approval rate of Bush’s handling of the
tragedy so that the result will be approximately within 5% of margin of error, how many voters should
USA Today survey?
(f) If CNN would like to conduct a poll to find out the approval rate of Bush’s handling of the tragedy so
that the result will be approximately within 1% of margin of error, how many voters should CNN
survey?
4. Lake pollution is a serious concern for the State of Michigan. Data from several previous years indicates that
30% of fish were not edible. The State took a Water Pollution Clean Up action two years ago. This year, a study
will be conducted to find out if the action works or not.
(a) In order to estimate the proportion of uneatable fish with the margin of error within 3%, how many fish
should the researcher sample?
(b) Suppose a random sample of 100 fish were inspected and were found that 28% not eatable. Determine a
95% confidence for the true proportion for this year’s fish population.