IMathAS-libretexts

To test whether or not the mean circuit board thickness is 12 mm with the new process, for which one of the following would neither the z-test nor the t-test be justified?

A random sample of 9 circuit boards is tested; the only available standard deviation is the one that is computed for the sample; and the histogram of the data is as shown above in histogram A.
A random sample of 40 circuit boards is tested; the only available standard deviation is the one that is computed for the sample; and the histogram of the data is as shown above in histogram B.
A random sample of 35 circuit boards is tested; the population standard deviation sigma is known; and the histogram of the data is as shown above in histogram C.
A random sample of 9 circuit boards is tested; the only available standard deviation is the one that is computed for the sample; and the histogram of the data is as shown above in histogram D.

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