a$.$ Calculate the mean value. $(2$ marks$)$

b$.$ Calculate $2$ sigma values. $(2$ marks$)$

c$.$ Use the estimate made in $($a & b$)$ to draw a I or X control chart for ranges with showing the center line $($CL$),$ upper and lower control limit $($UCL & LCL$).$ Plot the ten measurement unit. $(8$ marks$)$

d$.$ Comment on the current state of the process in $($c$).(2$ marks$)$

e$.$ What action, if any more than control limit$,$ what would you recommend on these case? $(2$ marks$)$

f$.$ Plot out the $3$ sigma normal distribution chart and comment it$.(4$ marks$)$