Ten samples of size four were taken from a process, and their weights measured. The sample averages and sample ranges are in the following table. Construct and plot an x-bar and R-chart using these data

Is the process in control?

Sample Mean Range
1 20.01 0.45
2 19.98 0.67
3 20.25 0.30
4 19.90 0.30
5 20.35 0.36
6 19.23 0.49
7 20.01 0.53
8 19.98 0.40
9 20.56 0.95
10 19.97 0.79

X-bar Range
x-doublebar value 20.024

R bar 0.524

Upper control limit 20.406 1.196
Center line 20.024 0.524
Lower control limit 19.642 0

The x-bar chart is out of control because samples 6 and 9 are outside of the control limit, and therefore the process is out of control.