The Mean of the Sample Means and the Pooled Standard $\bar{\bar { x }} = 420$

True/False

The mean of the sample means and the pooled standard deviation of 40 samples of size 9 taken from a production process under control are $\bar{\bar { x }} = 420$ ,and S = 12,respectively.The lower control limit and the upper control limit of the 3-sigma $\bar { x }$ chart are 408 and 432,respectively.