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MAT312
Study Guide – Chapter 9
Chapter 9 Confident Intervals for Two Samples
9.1 Comparing Two Means (Large, Independent Samples) x-bar1 - x-bar2 = -8
1. Describe independent samples. 9.2 F 95% S
N =42 39
2. Describe dependent samples. X-bar = 15 23
σ =4.7 5.2
3. What is confidence interval for two population means? (-10.16, -5.836)
Point estimator – E, Point estimator + E
4. What is margin of error for two large independent samples?
Page 514: 11, 13 & 14
9.2 Comparing Two Means (Small, Independent Samples) Population SDev is Unknown
2-SampTinterval Sample SDev = S =
5. What is margin of error for two small independent samples (variances not equal)?
6. Explain Pooled (Variances are Equal) and Not Pooled (Variance not Equal)
Page 525 & 527:14&19
9.3 Comparing Two Means (Dependent Samples) TInterval
7. Explain the term paired.
8. Explain paired differences. X2 – X1
Page 537: 9 & 11
9.4 Comparing Two Population Proportions 2PropZInterval
9. How to calculate the best Point Estimator? P-hat1 - P-hat2
10. How to calculate Margin of Error (E) from Confidence Interval?
Example 9.3 2 - SampZInterval
Additive 85% No Additive
N= 50 55
x-bar = 3250 3445
σ = 748 812
3250 – 3445 = -195
(-414.2, 24.16) Contains Zero = No Conclusion
Example 9.5 2 - SampTInterval
Her Class 90% Other Class
N = 11 9
x-bar = 75.0 82.0
s = 8.0 5.0
75.0 – 82.0 = -7
(-12.1, -1.899)
Example 9.6 Equal Variances
Took Reliever 99% Did not take
N= 12 20
x-bar = 5.6 6.3
s = 1.8 2.1
5.6 – 6.3 = -0.7
(-2.704, 1.3035) Contains Zero = No Conclusion
Example 9.10
Create List of Differences X2 – X1
TInterval (14.214, 19.386)
Example 9.13 2PropZInterval
A 90% B
X = 45 53
N = 76 78
(-0.2145, 0.03971)
Contains Zero = No Conclusion