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The per-store daily customer count (i.e., the mean number
of customers in a store in one day) for a nationwide convenience
store chain that operates nearly 10,000 stores has been
steady, at 900, for some time. To increase the customer count,
the chain is considering cutting prices for coffee beverages. The
question to be determined is how much to cut prices to increase
the daily customer count without reducing the gross margin on
Business Statistics: A First Course, Sixth Edition, by David M. Levine, Timothy C. Krehbiel, and Mark L. Berenson. Published by Prentice Hall.
Copyright © 2013 by Pearson Education, Inc.
Problems for Section 10.5 379
coffee sales too much. You decide to carry out an experiment in
a sample of 24 stores where customer counts have been running
almost exactly at the national average of 900. In 6 of the
stores, the price of a small coffee will now be $0.59, in 6 stores
the price of a small coffee will now be $0.69, in 6 stores, the
price of a small coffee will now be $0.79, and in 6 stores, the
price of a small coffee will now be $0.89. After four weeks of
selling the coffee at the new price, the daily customer count in
the stores was recorded and stored in .
a. At the 0.05 level of significance, is there evidence of a
difference in the daily customer count based on the price
of a small coffee?
b. If appropriate, determine which prices differ in daily customer
c. At the 0.05 level of significance, is there evidence of a
difference in the variation in daily customer count among
the different prices?
d. What effect does your result in (c) have on the validity of
the results in (a) and (b)?
10.62 Integrated circuits are manufactured on silicon wafers
through a process that involves a series of steps. An experiment
was carried out to study the effect on the yield of using three
methods in the cleansing step (coded to maintain confidentiality).
The results (stored in Yield-OneWay ) are as follows: