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a. Perform a test to determine if the means of the two data categories come
from population distributions with the same mean. What do you conclude
about the one-tail test and the two-tail test?
b. Create a histogram of the differences between the two series—Late minus
Early. Are there any insights that are evident?
23. Advanced Problem —Assume the Early and Late data in problem 21 is data
relating to energy drinks sold in a college coffee shop on individual days—on
day 1 the Early sales of energy drinks were 3 units and Late sales were 14 units,
etc. The manager of the coffee shop has just completed a course in data analysis
and believes she can put her new found skills to work. In particular, she believes
she can use one of the series to predict future demand for the other.
a. Create a regression model that might help the manager of the coffee shop
to predict the Late purchases of energy drinks. Perform the analysis and
specify the predictive formula.
b. Do you ﬁnd anything interesting about the relationships between Early and
c. Is the model a good ﬁt? Why?
d. Assume you would like to use the Late of a particular day to predict the
Early of the next day—on day 1 use Late to predict Early on day 2. How
will the regression model change?
e. Perform the analysis and specify the predictive formula.