An $\bar { x }$ Chart for a Normally Distributed Random Variable Has Control Limits

Multiple Choice

An $\bar { x }$ chart for a normally distributed random variable has control limits set at $\pm$ 3 standard errors from the centerline.One sample mean falls outside the control limits when the process is actually under control.The probability that this happened by chance is:

A) .997
B) .500
C) .050
D) .003