TUTORIAL 4
BIPS2212● PROBABILITY & STATISTICS
Department
:
Faculty of Information & Communication Technology
Program/class
:
BSCBIT-Y2S2 BSCIT-Y2S2 and BSCSM-Y2S2
Semester
:
2
Commence Date
:
Deadline Date
:
Unit Controller / Examiner
:
Contact Number
:
E-mail
:
Questions & Instructions:
ESTIMATION OF THE MEAN AND PROPOTION
1. 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 company took a sample of 25
comparable textbooks and collected information on their prices. This information
produced a mean price of M145 for this sample. It is known that the standard deviation
of the prices of all such textbooks is M35 and the population of such prices in normal.
(a) What is the point estimate of the mean price of all such college textbooks
(b) Construct a 90% confidence interval for the mean price of all such college textbooks
and interpret the results
2. In a 2009 survey by I-Pension LLC, adults with annual household incomes of M50,
000 to M125, 000 were asked about the average time they spend reviewing their
401(k) statements. Of the adults surveyed, about 72% said that they spend less than
5 minutes, and 27% said that they spend 5 to 10 minutes to review their 401(k)
statements. Suppose a random sample of 400 adults of all income levels who have
401(k) accounts were recently asked about the times they spend reviewing their
401(k) statements. The sample produced a mean of 8 minutes. Assume t hat the
standard deviation of such times for all 401(k) accounts holders is 2.20 minutes.
Construct a 98% confidence interval for the mean time spent by all 401(k) accounts
holders reviewing their 401(k) statements.
3. Dr. Moore wanted to estimate the mean cholesterol level for all adults’ men living in
Hartford. He took a sample of 25 adults men from Hartford and found that the men
cholesterol level for this sample is 186 mg/dL with a standard deviation of 12mg/dL.
Assume that t he cholesterol levels for all adults men in Hartford are (approximately)
Tutorial 4
normal distributed. Construct a 95% confidence interval for the population mean µ
and interpret the results
4. An alumni association wants to estimate the mean debts of this year’s college
graduates. It is known that the population standard deviation of the debts of this
year’s college graduates is M11, 800. How large a sample should be selected so that
the estimate with a 99% confidence level is within M800 of the population?
5. You want estimate the mean number of sentences in a magazine advertisement.
How many magazine advertisements must be included in the sample if you want to
be 95% confident that the sample mean is within one sentence of the population
mean?
6. You are running a political campaign and wish to estimate, with 95% confidence, the
proportion of registered voter who will vote for your candidate. Your estimate must
be accurate within 3% of the true population. Find the minimum sample size needed
if
(i)
No preliminary estimate is available
(ii)
A preliminary estimates is p  0.31
7. 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
M1450 and a standard deviation of M300 for such annual expresses. Determine a
99% confidence interval for the corresponding population mean.
8. According to a survey conducted by Pew Research Centre in June 2010, 44% of
people aged 18 to 29 years said that religion is very important to them. Suppose this
results is based on a sample of 1000 people aged 18 to 29 years
(a) State two conditions for a binomially distributed random variable
(b) What is the point estimate of the corresponding population proportion
(c) Find, with a 99% confidence level, the percentage of all people aged 18 to 28
years who will say that religion is very important to them. What is the margin of
error of this estimate
9. According to Harris Interactive survey of 2401 adults conducted in April 2009, 25% of
adults do not drink alcohol. Construct a 97% confidence interval for the corresponding
population proportion.
10. Lombard Electronics Company has just installed a new machine that makes a part that is
used in clocks. The company wants to estimate the proportion of these part produced by
this machine that are defective. The company manager wants this estimate to be within
0.02 of the population proportion for a 95% confidence level. What is the most
conservative estimate of the sample size that will limit the margin of error to within 0.02
of the population proportion?
Tutorial 4