Question

An important parameter of a process was measured by taking 25 samples. Each sample had 10 items in it. The average of the 25 sample means is given to be equal to 4.09, and the average of the 25 sample ranges is given to be equal to 0.34. Find the Upper Control Limit of the xbar chart.

		4.11
		4.14
		4.16
		4.19

Answer 1

Given : n=25 , $\bar{\bar{X}}=4.09$ , $\bar{R}=0.34$

Therefore , the upper control limit of the $\bar{X}$ chart is ,

$UCL=\bar{\bar{X}}+A_{2}\bar{R}=4.09+0.153*0.34=4.14$

Where , $A_{2}=0.153$ ; From statistical constants for control chart table