Sample Means and Ranges Were Obtained for Five Samples of 10

Multiple Choice

Sample means and ranges were obtained for five samples of 10 units per sample from a production process.Assume the process was considered to be in control during the period these samples were collected.The results are as follows: 1 10.58 .23
2 9) 97 .25
3 9) 99 .21
4 10.23 .28
5 10.23 .28
What is the central line of the X chart for this process

A) 10.00
B) 10.05
C) 10.20
D) 9.45
E) 9.75