Help Session IV: Practice Problems
1.
Thirty fast food restaurants including Wendy’s, Mc Donald’s, and Burger King were visited
during the summer of 2000 (The Cincinnati Enquirer, July 9,2000). During each visit, the
customer went to the drive through and ordered a basic meal such as a “combo” meal or a
sandwich, fries, and shake. The time between pulling up the menu board and receiving the filled
order was recorded. The time in minutes taken in each of the 30 visits are summarized below.
Descriptive Statistics: Time
Variable
N
N*
Mean
SE Mean
StDev
Minimum
Q1
Median
Q3
Maximum
Time
30
0
3.800
0.412
2.257
0.900
2.175
3.150
5.050
9.10
a.
Provide a point estimate of the population mean drivethrough time at fastfood
restaurants.
b.
At 95%, what is the margin of error?
c.
What is the 95% confidence interval estimate of the population mean?
2.
A wellknown credit card firm wishes to estimate the proportion of credit card holders who carry
a nonzero balance at the end of the month and incur an interest charge. Assume that the desired
margin of error is 0.03 at 98% confidence.
a.
How large a sample should be selected if it is anticipated that roughly 70% of the firm’s
card holders carry a nonzero balance at the end of the month?
b.
How large a sample should be selected if no planning value for the proportion could be
specified?
c.
How large (conservatively) a sample should be selected if it is anticipated that between
60 to 80 percent of the firm’s card holders carry a nonzero balance at the end of the
month?
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Playbill is a magazine distributed around the country to people attending musicals and other
theatrical productions. The mean annual household income for the population of Playbill readers
is $119,155 (Playbill, January 2006). Assume the standard deviation is 20700. A San Francisco
civic group has asserted that the mean income for the theater goers in the Bay Area is higher. A
sample of 60 theater attendees in the Bay Area showed that a sample household income of
$126,100.
a.
Develop hypotheses that can be used to determine whether the sample data support the
conclusion that the theater attendees in the Bay Area have a higher mean household
income than that for all Playbill readers.
b.
What is the pvalue based on the sample of 60 theater attendees in the Bay Area?
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 Spring '11
 Tawarmalani
 Statistics, Normal Distribution, Mean StDev SE, StDev SE Mean

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