The following table provides the costs for gasoline by

Chapter 15, Problem 116SE

(choose chapter or problem)

The following table provides the costs for gasoline by month in the United States over recent years and the percentage of the cost due to reining, distribution and marketing, taxes, and crude oil.  The table is from the U.S. Department of Energy Web site (http://tonto.eia.doe.gov/oog/info/gdu/gaspump.html). There is some concern that the reining or distribution and marketing percentages of the retail price have shown patterns over time.

(a)  Construct separate control charts for the refining  percentage of the retail price and the distribution and marketing percentage of the retail price. Use control charts for individual measurements. Comment on any signs of assignable causes on these charts.

(b)  Construct a control chart for the crude oil percentage of the retail price. Use a control chart for individual measurements. Comment on any signs of assignable causes on this chart.

(c) Another way to study the data is to calculate refining, distribution and marketing, and tax as costs directly.

The costs of these categories might not depend strongly on the crude oil cost. Use the percentages provided in the table to calculate the cost associated with refining and distribution and marketing each month. Construct separate control charts for refining and distribution and marketing costs each month. Use control charts for individual measurements. Comment on any signs of assignable causes on these charts and comment on any differences between these charts and the ones constructed in part (a).