In: Statistics and Probability
A process produces components with mean tensile strength of 85 MPa and standard deviation of 13 MPa. If the lowest acceptable strength is 40 MPa, what ppm of samples would be defective?
Solution:
Given:
A process produces components with mean tensile strength of 85 MPa and standard deviation of 13 MPa.
Mean =
Standard deviation =
The lowest acceptable strength is 40 MPa.
We have to find ppm of samples that would be defective.
First find:
P( X < 40 ) =...........?
Find z score for x = 40
Thus we get:
P( X < 40 ) =P( Z < -3.46 )
Look in z table for z = -3.4 and 0.06 and find corresponding area.
P( Z < -3.46 ) = 0.0003
Thus
P( X < 40 ) =P( Z < -3.46 )
P( X < 40 ) = 0.0003
We have to find ppm ( parts per million) of samples would be defective.
ppm of samples would be defective = 1,000,000 X 0.0003
ppm of samples would be defective = 300