In establishing control charts for a process, it is often essential to use both the x-bar chart and the R chart. Which of the following statements explain what these charts show? The x-bar_chart tells us the behavior of sample mean and the R chart tells us whether or not the x-bar chart is within control. The R chart tells us the behavior of sample variability and the x bar chart tells us whether or not the R chart is within control. The x bar chart tells us the behavior of sample mean and the R chart tells us the behavior of sample variability. The R chart is an alternative approach to measure the number of defective units in a process. None of the above statements is an acceptable explanation