When is a z test used and when is t test used.

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Z test is used when sample size is large and population standard deviation is known. T test is used when sample size is small or population standard deviation is unknown.

Z test is used for hypothesis testing when sample size is large (n > 30) and population standard deviation is known.
T test is used when sample size is small (n < 30) or population standard deviation is unknown.
Z test is used for comparing means of two populations when the population standard deviation is known.
T test is used for comparing means of two populations when the population standard deviation is unknown.
Example: Z test can be used to determine if the mean height of students in a school is significantly different from the national average height, given the population standard deviation.

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When is a z test used and when is t test used.

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