
1Sample ZIntervals
Worksheet 1 Solutions
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 Solutions.
 The margin of error is 0.10. The CI is
(35.18, 35.38).
 The procedure of forming 95% CIs
has 95% reliability. That is, 95% of all
samples result in an interval that covers
the true (population) mean. So, you are
95% confident that the true mean is
between 35.18 and 35.38.
 (35.12, 35.44)
 Higher confidence requires a larger
margin of error.
 The margin of error is 0.20. The CI is
(35.03, 35.43).
 When the sample size is increased by a
factor of 4, the margin of error
decreases by a factor of 2 (the square
root of 4).
 Solutions.
 The playing time of a CD Jill owns.
 All Jill's CDs (or the playing times of
each of Jill's CDs).
 The mean playing time of all her CDs; the
greek letter m
is used for this.
 47.927
 The margin of error is 2.87. The CI is
(45.06, 50.80).
 The procedure of forming 90% CIs
has 95% reliability. That is, 90% of all
samples result in an interval that covers
the true (population) mean. So, you are
90% confident that the mean playing time
of all Jill's CDs is between 45.06 and
50.80 minutes.
 The type of music Jill listens to has a
lower mean playing time than is the mean
playing time of all CDs.

