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Practice Chapter 8

1. Find zα/2 for the following levels of α:

a. α=.15

b. α=.20

c. α=.04

d. α=.08

e. α=.25

2. Find zα/2 for the following confidence levels:

a. 80%

b. 75%

c. 60%

d. 94%

e. 99%

3. Construct a 90% confidence interval for the mean of a normal population if a random sample of size 40 from the population yields a sample mean of 75 and the population has a standard deviation of 5.

4. Thirty panels were exposed to various corrosive conditions to measure the protective ability of paint. The mean life for the samples was 168 hours. The life of the paint samples is assumed to be normally distributed with a population standard deviation of 30 hours. Find the 95% confidence interval for the mean life of the paint.

5. Find the t – value such that .01 area of the area under the curve is to the right of the t – value. Assume the degree of freedom is 21.

6. Find tα/2,n-1 for the following combinations of α and n.

a. α=.05, n=15

b. α=.20, n=20

c. α=.01, n=12

d. α=.10, n=18

e. α=.02, n=25

7. Construct an 80% confidence interval for the mean of a normal population assuming that the values listed below comprise a random sample taken from the population The population standard deviation is unknown.

8. Local newspaper conducted a poll of 1,000 randomly selected readers to determine their concerns about the handling of trash removal. The paper found that 650 readers confirmed positively about the trash removal.

a. Compute the best point estimate for the percentage of readers who confirmed positively.

b. Construct a 90% confidence interval for the fraction

c. What conclusions can be inferred from the confidence interval?