c. If the students had taken a random sample of 100 cups (all other info staying the same)
how would this affect the margin of error?
It would decrease
d. What sample size is needed if the students wanted the margin of error to be at most .02
ounces per cup?
n =
2
02
.
24
.
96
.
1
x
=553.19; so at least 554 cups of coffee are needed
3. To estimate the number of visitors per month to the John F. Kennedy Library, the
number of visitors was recorded for randomly selected months. Descriptive statistics on
the sample data are shown below. Assume standard deviation for number of visitors stays
at 35,000 people.
Descriptive Statistics: Visitors
Total
Variable
Count
Mean
Visitors
36
250926
a. Estimate the average number of visitors to the JFK library.
95% confidence interval for the mean number of visitors per month is
250,926
= 11,433 = between 239,493 and 262,359 visitors.
b. Using your answer to part a, what would be an unusually average for a given year?
What would be an unusually low average number of visitors for a given year? Why?
2

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An usually high average would be one that is above 262,359. The higher the value
the more unusual. An unusually low average would be one that is below 239,493; the
lower the value the more unusual.
4. A group of randomly selected 50 sales representatives from a company had an average
sales of $107.5 million this year. (Assume the standard deviation of sales is stable at
$20.5 million.)
a. Use your data to find
a range of likely values for average sales for the entire company.

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