# MTH 380 Lecture Notes - Lecture 9: Point Estimation, Variance, Standard Deviation

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1

ASSIGNMENT 9, Estimating the difference between two population means and two

population proportion

Part 1

Chapter 8, Large - Sample estimation

Ch.8.4. Estimating the difference between two population means

1.Ch.8.4, 1 & 3, p.311

Independent random samples were selected from two quantitative populations. The

sample sizes, sample means and variances are given in the table below:

Population

1 2

_______________________________________________

Sample size 35 49

Sample mean 9.7 7.4

Sample variance 10.78 16.44

Find 90% and 99% confidence intervals for estimating the difference in population means.

Can you conclude with 90% confidence that there is a difference in the means for the two

populations? With 99% confidence?

2. Ch.8.4, Review, 3, p.330

Independent random samples of

150

n

=

and

260n=

observations were selected

from populations 1 and 2, respectively. The sample sizes and computed sample statistics

are given in the table:

Population

1 2

_______________________________________________

Sample size 50 60

Sample mean 100.4 96.2

Sample variance 0.8 1.3

Find 90% confidence intervals for the difference in population means.

Suppose you wish to estimate

12

µµ

−

correct to within 0.2, with probability equal to 0.95.

If you plan to use equal sample sizes, how large should

1

n

and

2

n

be?

2

3. Ch.8.4, 11, p.311

4. Ch.8.4, 12, p.311