The upper and lower specifications for a service are 10 min. and 8 min., respectively. The process standard deviation is 0.25 min. and the process average is 9 min. What conclusion can be drawn?
A) The process is capable.
B) The process is not capable because the process average is out of control.
C) The process is not capable because the process variability is too great.
D) The specifications should be changed to 9.75 and 8.25, respectively.

Question

Quizplus · Accepted Answer

The process capability index (Cpk) can be calculated to determine if the process is capable. Cpk = min[(USL - mean)/(3*σ), (mean - LSL)/(3*σ)] = min[(10-9)/(3*0.25), (9-8)/(3*0.25)] = min[1.33, 1.33] = 1.33. Since Cpk is greater than 1, the process is capable.

The Upper and Lower Specifications for a Service Are 10