Answer:
1) cpk < 1.33, therefore it is not capable
b) cpk = 1.33, therefore it is capable
c) cpk < 1.33, therefore it is not capable
2) Cpk can never be greater than the Cp, but can be equal to it
Step-by-step explanation:
Upper limit (USL) = 47 minutes and Lower limit (LSL) = 30 minutes
1)
a) mean (μ) = 37 minutes, standard deviation (σ) = 3 minutes
[tex]cpk=min(\frac{USL-\mu}{3\sigma}, \frac{\mu - LSL}{3\sigma})=min(\frac{47-37}{3*3},\frac{37-30}{3*3} )=min(1.11,0.78)=0.78[/tex]
[tex]cp=(\frac{USL-LSL}{6\sigma})=\frac{47-30}{6*3}=0.94[/tex]
cpk < 1.33, therefore it is not capable
b) mean (μ) = 38 minutes, standard deviation (σ) = 2 minutes
[tex]cpk=min(\frac{USL-\mu}{3\sigma}, \frac{\mu - LSL}{3\sigma})=min(\frac{47-38}{3*2},\frac{38-30}{3*2} )=min(1.5,1.33)=1.33[/tex]
[tex]cp=(\frac{USL-LSL}{6\sigma})=\frac{47-30}{6*2}=1.42[/tex]
cpk = 1.33, therefore it is capable
c) a) mean (μ) = 38.5 minutes, standard deviation (σ) = 2.9 minutes
[tex]cpk=min(\frac{USL-\mu}{3\sigma}, \frac{\mu - LSL}{3\sigma})=min(\frac{47-38.5}{3*2.9},\frac{38.5-30}{3*2.9} )=min(0.98,0.98)=0.98[/tex]
[tex]cp=(\frac{USL-LSL}{6\sigma})=\frac{47-30}{6*2.9}=0.98[/tex]
cpk < 1.33, therefore it is not capable
2) Cpk can never be greater than the Cp, but can be equal to it
