If the population is normal and its standard deviation, σ, is unknown and the sample size, n, is large (n ≥ 30), interval estimates for the population mean must be determined using z values.

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Quizplus · Accepted Answer

When the population standard deviation is unknown and the sample size is large, the t-distribution is typically used for interval estimates of the population mean, although the z-distribution can be used as an approximation.

If the Population Is Normal and Its Standard Deviation, σ