The individual observations are plotted by time $($i$.$e$.$ observations $1-24).$ The upper and lower

control limits based on required tolerances for the center hole diameter are shown by the

horizontal lines. Looking at this graph, answer the following questions:

a$)$ What if anything should be done at observation $6?$

b$)$ At what point $($which sample #$)$ should the QC Lab alert manufacturing that the process

may be out of control or nearly so$?$

c$)$ Did this process actually become out of control and if so how many parts potentially may

need to be scrapped?

d$)$ What could account for the sudden change between samples $23$ & $24$