Question: Grand foods, Inc., makes energy supplement bars for use by athletes and others who need an energy boost. One of the critical quality characteristics is the weight of the bars. Too much weight implies that too many liquids have been added to the mix and the bar will be too chewy. If the bars are light, the implication is that the bars are too dry. To monitor the weights, the production manager wishes to use process control charts. Data for 30 subgroups of size 4 bars are contained in the file Grandfoods. Note that a subgroup is selected every 15 minutes as bars come off the manufacturing line.
a. Use these data to construct the appropriate process control chart(s).
b. Discuss what each chart is used for. Why do we need both charts?
c. Examine the control charts and indicate which, if any, of the signals are present. Is the process currently in control?
d. Develop a histogram for the energy bar weights. Discuss the shape of the distribution and the implications of this toward the validity of the control chart procedures you have used.