You want to determine the lower control line for a p-chart for quality control purposes.You take several samples of a size of 50 items in your production process.From the samples, you determine the fraction defective is 0.006 and the standard deviation is 0.001.If the desired confidence level is 99.7 percent, which of the following is the resulting LCL value for the line?
A)0.0
B)0.002
C)0.003
D)0.004
E)None of these

Question

Quizplus · Accepted Answer

The formula for calculating the lower control line (LCL) for a p-chart is:

LCL = P - 3 * sqrt((P*(1-P))/n)

where P is the proportion defective, n is the sample size, and sqrt is the symbol for square root.

Substituting the given values, we get:

LCL = 0.006 - 3 * sqrt((0.006*(1-0.006))/50)
LCL = 0.003

Therefore, the resulting LCL value for the line is 0.003. The correct choice is C.

You Want to Determine the Lower Control Line for a P-Chart