A company wants to reduce the wait time for service
Four customers are selected randomly each day and find the total time that each customer waits (in minutes) while their machine is serviced
Next, from these four observations, the sample average and range are found.
This process is repeated for 25 days.
The summary data for these observations are
The sum of X, from X=1 to 25; Xbar = 1000
The sum of R, from R=1 to 25; Rbar = 250
A- find X bar and R chart control limits
B- Assuming the process is in control and that a desirable value on the upper bound of the waiting time is 50 minutes, how many customers will have to wait more than 50 minutes
C- To reduce the waiting time of customers, the manager hires additional service techs, which reduces the average service time to 35 minutes.
What portion of customers will still have to wait more than 50 minutes if the variability in service times is the same as before.