Stats for Business HOMEWORK 9
(29 problems for Topic 7: Confidence Intervals)
DIRECTIONS:
• For precision, make calculations without rounding.
There are several ways to do this. The TI graphing calculators let you reference ANS (the
previous answer.) Every calculator has a memory button for which you can google directions.
Or you can choose to simply “write down all the numbers” if you’d prefer not to use the
memory button.
Then write final answers for proportions to four decimal places (e.g. 0.6476 or 64.76%) and
for dollar amounts to the nearest cent (e.g. $10.76.)
• The specific directions below note a few exercises for which you can use either a calculator
or MINITAB in the computer lab in 41 SH to calculate x̄ and s, whichever you prefer. (On
exams and quizzes, you’ll need to use a calculator since MINITAB won’t be available.)
• Stop by either of the two tutor labs (Stats Lab and SWAT) or TA/prof office hours for discussion and consultation.
Initial Exercises Based on Means Problems
• Exercise 6.1 (page 338)
Answer these specific questions:
(a) In statistics terminology, what descriptive letter is attached to the number $220?
(b) What descriptive letter is attached to the number 100?
(c) What’s the standard deviation of x̄?
(d) $220 would be the correct value of the standard deviation of x̄ for which sample size?
• Exercise 6.2
(Recall that the textbook calls the Bell Curve Rule the “68-95-99.7 Rule.”)
• Exercise 6.3
• Exercise 6.4
◦ By SRS the textbook means “simple random sample.”
◦ Open a browser to the textbook website:
bcs.whfreeman.com/psbe3e
and click “Statistical Applets” under “Browse By Category”
◦ Click the third applet in the list: “Confidence Interval”
◦ Follow the instructions in parts (a) and (b) of Exercise 6.4.
(continued)
1
Confidence Intervals for Proportions
• Exercise 8.1 (page 459)
• Exercise 8.3
• Exercise 8.2
• Exercise 8.4
• Exercise 8.13
• Exercise 8.14
• Exercise 8.29
Add parts (b) and (c):
(b) Find an 80% confidence interval for the proportion of all college students who have at
least one credit card.
(c) Which is more precise, the 80% CI or the 95% CI? Explain.
• Exercise 8.30
• Exercise 8.37
Add part (b):
(b) Would the data support an advertisement by the company that it ships 95% of orders
on time?
• Exercise 8.39
Add part (b):
(b) Are more than 70% of first-year students at this university concerned about being financially well-off?
• Exercise 8.43
Ignore the book’s instructions about p∗ . Use the formula in the Topic 7 Notes
instead.
• Exercise 8.49
Confidence Intervals for Means
• Exercise 7.1 (page 397)
• Exercise 7.3
• Exercise 7.4
• Exercise 6.5 (page 341)
• Exercise 6.6
(continued)
2
• Exercise 6.7
• Exercise 6.8
• Exercise 6.9
Exercise 6.9 is a puzzler. If you can’t figure out these answers quickly it’s okay to
look at the HW9 key to discover the answers! ,
• Exercise 6.27 (page 350)
(Assume that the sample standard deviation is s = 3.2 years.)
• Exercise 6.28
◦ Ignore the book’s instructions to “assume the standard deviation is $21.00.” Instead,
calculate the sample mean x̄ and sample standard deviation s.
◦ It might save time to stop by computer lab 41 SH to use MINITAB rather than your
calculator (though the choice is yours.) As a reminder, the MINITAB commands are
Stat > Basic Statistics > Display Descriptive Statistics
(The data set Shoppers is found on the Homework page of the Stats website.)
• Exercise 6.29
◦ Ignore the book’s instructions to “use $22.00 for the standard deviation” and instead
use the actual standard deviation s from Exercise 6.28.
• Exercise 7.30 (page 414)
Ignore parts (a) and (b). Do part (c) and add part (d):
(d) Nonprofit organizers claim that gross sales averaged at least $1800 in 2008. Is this claim
plausible?
• Exercise 7.23
The MINITAB data set Mileage is available if you prefer to calculate x̄ and s with MINITAB
instead of using your calculator. Also add parts (b) and (c), both with 95% confidence:
(b) Toyota’s sales literature says that the Highlander averages at least 32 mpg at 60 mph.
Is that plausibly true for the car being tested?
(c) Is that definitely true for the car being tested?
(end of assignment)
3