Download 1 True-False. One can reduce the width of a confidence interval by

Name: __________________
1
Class:
Date: _____________
True-False.
One can reduce the width of a confidence interval by taking a smaller sample size.
2
True-False.
A 95% confidence interval estimate for a population mean 80%, the confidence interval for becomes narrower.
3
is determined to be 75 to 85. If the confidence level is reduced to
A survey of 100 retailers revealed that the mean after-tax profit was $80,000. If we assume that the population standard deviation
is $15,000, determine the 95% confidence interval estimate of the mean after-tax profit for all retailers.
_________
4
The temperature readings for 20 winter days in Grand Rapids, Michigan are normally distributed with a mean of 5.5 degrees and
a standard deviation of 1.5. Determine the 90% confidence interval estimate for the winter mean temperature.
_________
5
An economist is interested in studying the incomes of consumers in a particular region. The population standard deviation is
known to be $1,000. A random sample of 50 individuals resulted in an average income of $15,000. What is the upper end point in
a 99% confidence interval for the average income?
Enter your answer to the nearest cent.
_________
6
The sample size needed to estimate a population mean within 2 units with a 95% confidence when the population standard
deviation equals 8 is:
a. 9
7
d. 8
b. 165
c. 164
d. 163
The sample size needed to estimate a population mean to within 10 units was found to be 68. If the population standard deviation
was 50, then the confidence level used was:
a. 99%
9
c. 62
To estimate with 99% confidence the mean of a normal population, whose standard deviation is assumed to be 6 and the
maximum allowable sampling error is assumed to be 1.2, requires a random sample of size:
a. 166
8
b. 61
b. 95%
c. 90%
d. 80%
True-False.
In determining the sample size n needed to estimate the population mean, n decreases as the population standard deviation decreases.
PAGE 1
Name: __________________
Class:
Date: _____________
10 A random sample of 10 college students was drawn from a large university. Their ages are 22, 17, 27, 20, 23, 19, 24, 18, 19, and
24 years. Estimate the population mean with 90% confidence.
_________
11 A confidence interval was used to estimate the proportion of international students. A random sample of 72 students generated
the following 90% confidence interval: (0.438, 0.642). Using the information above, what size sample would be necessary if we
wanted to estimate the true proportion to within 0.08 using 95% confidence?
a. 105
b. 150
c. 420
d. 597
12 A sample of 150 students at a particular college showed that 45 students favor pass-fail elective courses. Provide a 95%
confidence interval estimate of the proportion of the population of students who favor pass-fail grades for elective courses.
_________
Enter your answer in the form (LL,UL) where LL= lower class limit and UL = upper class limit. Include the parentheses. Enter your
answers to three decimal places
PAGE 2
ANSWER KEY
Lueker Summer2008 HW7
1. False
2. True
7. a
8. c
ANSWER KEY - Page 1
3. ( $77060,$82940 )
9. True
( 4.9483,6.0517 )
10. ( 19.446,23.154 )
4.
5. $15364.16
6. c
11. b
12. ( 0.227,0.373 )