Nancy, Inc. manufactures 4 ounce chocolate bars. Random samples of size four were taken and weighed. Eight hours of observation provided the following data.
Sample Mean Range
1 4.01 0.14
2 4.03 0.18
3 3.98 0.16
4 4.20 0.17
5 3.89 0.13
6 4.00 0.18
7 4.05 0.17
8 4.03 0.16
9 4.08 0.15
a. Determine the 3 sigma upper and lower control limits for the x-bar chart.
b. Determine the 3 sigma upper and lower control limits for the R-chart.