8. Control charts for X and S are maintained on the shear strength of spot welds.

After 30 subgroups of size 4,



X i = 12,660 and



Si = 500. Assume that the process is in control.

(a) What are the X -control limits?

(b) What are the S-control limits?

(c) Estimate the standard deviation for the process.

(d) If the minimum specification for this weld is 400 pounds, what percentage of the welds will not meet the minimum specification?