Samples of 20 parts from a metal grinding process
are selected every hour. Typically, 2% of the parts
needs rework.
• Let X denote the number of parts in the sample of 20
that require rework.
• A process problem is suspected if X exceeds its mean
by more than 3 standard deviations.
• Using a spreadsheet, simulate 30 hours of the
process, that is, 30 samples of size 20, and estimate
the chance that X exceeds its expected value by more
than 3 standard deviations.
.