# 1-Sample Z-Intervals

## Worksheet 1 Solutions

Back to the exercises

1. Solutions.
1. The margin of error is 0.10. The CI is (35.18, 35.38).
2. 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.
3. (35.12, 35.44)
4. Higher confidence requires a larger margin of error.
5. The margin of error is 0.20. The CI is (35.03, 35.43).
6. 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).
2. Solutions.
1. The playing time of a CD Jill owns.
2. All Jill's CDs (or the playing times of each of Jill's CDs).
3. The mean playing time of all her CDs; the greek letter m is used for this.
4. 47.927
5. The margin of error is 2.87. The CI is (45.06, 50.80).
6. 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.
7. The type of music Jill listens to has a lower mean playing time than is the mean playing time of all CDs.