AP Statistics Practice Free Response Test – Chapter 8: Estimating with Confidence
1. A 2005 report by the American Management Association summarized the results of an
extensive survey given to 526 randomly selected U.S. businesses. One of the questions asked
was whether the company had fired any employees for misuse of the Internet while at work.
The report gave a confidence interval of .229 to .292 for the proportion of all U.S. companies
that have fired employees for misuse of the Internet while at work.
(a) What proportion of the businesses in the sample had answered yes to this question?
(b) What was the margin of error for this interval?
(c) Explain to someone who does not know anything about statistics why we can’t simply
say that the answer to part (a) is true for all U.S. businesses.
2. A random sample of 1100 teenagers (ages 12 to 17) was asked whether they played games
online; 775 said that they did.
(a) Verify that the conditions are met here for inference about a population proportion p.
(b) Construct and interpret a 99% confidence interval for the population proportion p.
(c) How large a sample would you need to take to estimate p within 2% at a 99% confidence
level? Use
ˆ
p
for the value of p*. Show your work.
3. Rocky Mountain Airlines Flight 441 flies from Denver to Albuquerque each day at 8:00 am.
The flight is listed as taking 58 minutes, on average. A random sample of 9 of these flight
times, rounded to the nearest minute, is given in the table below.
56
62
59
58
60
57
59
61
62
(a) Construct a 95% confidence interval for the true mean flight time for Flight 441.
(b) Does the interval in (a) give you reason to suspect that the claim of 58 minutes is false?
Explain.
(c) What concern do you have about the data used here to construct the confidence interval
in part (a)? Explain.
