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The diameter of 3.5-inch compact discs is normally distributed. Periodically, quality control inspectors at Dallas Discs randomly select a sample of...
The diameter of 3.5-inch compact discs is normally distributed. Periodically, quality control inspectors at Dallas Discs randomly select a sample of 16 discs. If the mean diameter of the discs is too large or too small, the disc punch is shut down for adjustment; otherwise, the punching process continues.
Why do i have to use a T-Test and NOT a Z-Test for this question? I mean i know from the 1st sentence that it is NORMALLY distributed? Is there a general rule when I have to use Z-Tests and when T-Tests for hypothesis tests of the Pop. mean?
