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# Confidence Interval Estimate

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Question 1

Sample with size n = 100 has mean = 30. Assuming the population standard deviation is 8, construct 95% confidence interval for population mean. Use formula on page 312, z?/2 = 1.96

between 28.4 and 31.6

between 27.0 and 33.0

between 26.1 and 34.2

between 24.1 and 35.9

Question 2

With sample mean x = 12.5, sample size n = 40 and population standard deviation = 4
find 99% confidence interval for population mean. Use formula on page 312 with z?/2 = 2.575

between 11.5 and 13.5

between 10.9 and 14.1

between 10.1 and 15.1

between 7.4 and 14.2

Question 3

Find t-value for sample size n = 16 and area to the right 0.10 (Use Appendix Table IV).

2.015

1.860

1.725

1.341

Question 4

For sample mean x = 150, sample size n = 36 and sample standard deviation s = 40 find 80% confidence interval for population mean. Population standard deviation is not known, you should use formula on page 328 with t-value from Appendix Table IV (use column t0.10).

135.6 to 148.4

154.2 to 175.8

141.3 to 158.7

162.3 to 187.5

Question 5

Use formula from material posted on Blackboard in for this week Lectures section to estimate population proportion. Sample proportion is ps = 0.48, sample size 125, zc = 1.96 (90% confidence level).

0.26 to 0.64

0.39 to 0.57

0.41 to 0.52

0.28 to 0.71