Download 6.1-6.2-reivew-2014

Statistics
6.1-6.2 Review
Name: __________________
For #1-4, use the standard normal table or t-distribution table to find the critical value for
each.
1. Find t c if n = 18 and c = 0.95.
2. Find z c if c = 0.94.
3. Find z c if c = 99.5%.
4. Find t c if d.f. = 9 and c = 0.90
Find the margin of error, E, given the information below.
5. n = 6, s = 3 and c = 0.99
6. c = 0.80, n = 75 and   2.5
7. Find E from the confidence interval (21.61, 30.15)
For #8-11, find the sample size needed for the given margin of error.
8. c = 0.90, s = 6.8 and E = 1
9. c = 0.95, s = 2.5 and E = 1
10. c = 0.99, s = 2.8 and E = 3
11. c = 0.94, s = 5.4 and E = 3
12. How does the sample size change when the confidence level changes?
For #13-21, decide if you would use the normal distribution, a t-distribution, or neither to
create a confidence interval using the given information.
13. From a population that is approximately normal, n = 40 and s  2.8
14. From a population that is normally distributed, with n = 24 and  is unknown.
15. A sample with size n = 10 and   5 .
16. A sample of size 12, in which the x  57.79, s = 19.05, and we can assume the population is
approximately normal.
17. A publishing company has just published a new college textbook. Before the company
decides the price at which to sell this textbook, it wants to know the average price of all such
textbooks in the market. The research department at the company took a sample of 25
comparable textbooks and collected information on their prices. This information produced a
mean of $90.50 for this sample. It is known that the standard deviation of the prices of all such
textbooks is $7.50 and the population of such prices is normally distributed.
18. A random sample of 22 people were selected and asked how many miles they drive per year.
The mean miles driven were 15,285 with a standard deviation of 1,062 miles.
19. Dr. Moore wanted to estimate the mean cholesterol level for all adult men living in Hartford.
He took a sample of 25 adult men from Hartford and found that the mean cholesterol level for
this sample is 186 with a standard deviation of 12. Assume that the cholesterol levels for all
adult men in Hartford are approximately normal.
20. Sixty-four randomly selected adults who buy books for general reading were asked how
much they usually spend on books per year. The sample produced a mean of $1450 and a
standard deviation of $300 for such annual expenses.
21. According to USA Today (July 1, 2005), the mean bank credit card debt for households was
$7868 in 2004. Assume that this mean was based on a random sample of 900 households and
that the standard deviation of such debts for all households in 2004 was $2070.
Create a confidence interval using the given information. You will have to first determine
if the normal distribution or t-distribution should be used. Assume that the samples come
from a population that has a normal distribution.
22. Construct a 99% confidence interval for a data set obtained from a sample in which n = 20,
x  24.5 and   3.1
23. Construct a 95% confidence interval for the data set below: A company randomly selects 9
employees and monitors the time in hours they spent on their computer for non-job related
activities. The times are: 7, 12, 9, 8, 11, 4, 14, 1, 6
24. Construct a 95% confidence interval for the population mean,  . Assume the population
has a normal distribution. A sample of 20 college students had mean annual earnings of $3120
with a standard deviation of $677.
25. The GPA of 10 randomly selected high school students are listed below. Assume the GPA’s
are normally distributed. 2.0 3.2 1.8 2.9 0.9 4.0 3.3 2.9 3.6 0.8.
Find a 98% confidence interval for the true mean.