Please help me with this question:
Assuming the variation of the width of each disk in a stack of three disks is normally distributed with a standard deviation of 1 inch, and a specified tolerance for the width of each disk is set at three standard deviation, their statistical tolerance for the width of a stack of three disks would be most nearly which of the followings? The answer is 5.20 inches; How?
TIP: If they are talking about tolerance or specification, you need the standard deviation of the distribution of individuals of the population. If you are talking about standard deviation of samples, like subgroups on control charts you use the standard deviation of samples.
This Standard Error of the Mean*, where the standard deviation of samples is equal to the standard deviation of the population divided by the square root of the sample size, is very useful on other ASQ questions.
*Ignoring the "Finite Correction Factor".