AARP reported on a study conducted to learn how long it takes individuals to pre
ID: 1099299 • Letter: A
Question
AARP reported on a study conducted to learn how long it takes individuals to prepare their federal
income tax return (AARP Bulletin, April 2008). The data contained in the companion data le are
consistent with the study results. These data provide the time in hours required for 40 individuals to
complete their federal income tax returns. Using past years data, the population standard deviation
can be assumed known with = 9 hours.
a. What is the 90% condence interval estimate of the mean time it takes an individual to complete
a federal income tax return?
b. Develop a 95% condence interval estimate of the population mean.
c. Develop a 99% condence interval estimate of the population mean.
d. Discuss what happens to the width of the condence interval as the condence level is increased.
Does this result seem reasonable? Explain.
Return Preparation Time(Hours)
35.3
30.5
37.4
26.5
13.0
49.9
28.8
44.0
61.6
0.5
40.5
34.9
47.9
36.6
24.1
39.8
47.8
18.5
36.6
39.2
14.5
37.3
40.5
49.3
45.5
28.3
19.5
5.6
52.6
41.4
45.3
39.0
33.7
29.4
14.5
40.1
33.7
36.9
5.6
33.7
Return Preparation Time(Hours)
35.3
30.5
37.4
26.5
13.0
49.9
28.8
44.0
61.6
0.5
40.5
34.9
47.9
36.6
24.1
39.8
47.8
18.5
36.6
39.2
14.5
37.3
40.5
49.3
45.5
28.3
19.5
5.6
52.6
41.4
45.3
39.0
33.7
29.4
14.5
40.1
33.7
36.9
5.6
33.7
Explanation / Answer
Observed Mean (