12. A company that manufactures oil seals found the population mean to be 49.15 mm (1.935 in.), the population standard deviation to be 0.51 mm (0.020 in.), and the data to be normally distributed. If the internal diameter of the seal is below the lower specification limit of 47.80 mm, the part is reworked. However, if it is above the upper specification limit of 49.80 mm, the seal is scrapped.

(a) What percentage of the seals is reworked? What percentage is scrapped?

(b) For various reasons, the process average is changed to 48.50 mm. With this new mean or process center, what percentage of the seals is reworked? What percentage is scrapped? If rework is economically feasible, is the change in the process center a wise decision?