Consider Process Data Consisting of the Amounts of Potato Chips $\bar { x }$

Consider process data consisting of the amounts of potato chips (in ounces) in randomly selected bags of chips. The process is to be monitored with $\bar { x }$ control charts based on samples of 50 bags randomly selected each day for 15 consecutive days of production. What does $\bar { x }$ denote?

A) The mean of the standard deviations for the 15 days.
B) The mean of the ranges for the 15 days.
C) The mean of 50 bags.
D) The mean of all 15 sample means.