Instruction 18-7
a Factory Supervisor Is Concerned That the Time

Instruction 18-7
A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds) is too erratic and adversely affects expected profits. The supervisor proceeds by randomly sampling five individuals per hour for a period of 10 hours. The sample mean and range for each hour are listed below.
She also decides that lower and upper specification limit for the critical-to-quality variable should be 10 and 30 seconds, respectively.
$$\begin{array} { | l | l | l | } \hline \text { Hour } & \underline { \underline { X } } & \underline { R } \\\hline 1 & 18.4 & 25 \\\hline 2 & 16.9 & 27 \\\hline 3 & 23.0 & 30 \\\hline 4 & 21.2 & 23 \\\hline 5 & 21.0 & 24 \\\hline 6 & 24.0 & 25 \\\hline 7 & 19.3 & 12 \\\hline 8 & 15.8 & 14 \\\hline 9 & 20.0 & 13 \\\hline 10 & 23.0 & 11 \\\hline\end{array}$$
-Referring to Instruction 18-7,suppose the supervisor constructs an R chart to see if the variability in collection times is in control.What is the centre line of this R chart?

A) 20.40
B) 20.56
C) 20.00
D) 24.00