XYZ manufacturing has received an order to produce a rod 5 inches in diameter + .04 inch. In sample runs, the machine tool that will be making the rod has been able to produce rods with a mean diameter of 4.99 inches and a standard deviation of 0.011 inch. The process capability ratio for this process is
A) -1.44
B) -1.21
C) 1.21
D) 1.44

Question

XYZ manufacturing has received an order to produce a rod 5 inches in diameter + .04 inch. In sample runs, the machine tool that will be making the rod has been able to produce rods with a mean diameter of 4.99 inches and a standard deviation of 0.011 inch. The process capability ratio for this process is
A) -1.44
B) -1.21
C) 1.21 
D) 1.44

Quizplus · Accepted Answer

The process capability ratio (PCR) is given by:
PCR = (upper specification limit - lower specification limit) / (6 * standard deviation)

Here, the upper specification limit = 5.04 inches, the lower specification limit = 4.96 inches, the standard deviation = 0.011 inch, and the mean = 4.99 inches.

So, PCR = (5.04 - 4.96) / (6 * 0.011) = 1.21

Hence, the answer is C.

XYZ Manufacturing Has Received an Order to Produce a Rod