Question

Which test is used when the sample size is more than $30$?

Answer 1

Z-test is the best fit when the sample size is more than $30$.

This is due to the central limit theorem that as the sample size increases, the samples are considered to be distributed normally.

A z-score gives us an idea of how far from the mean a data point is

Formula:

$zscore=\frac{\left(x-\mu \right)}{\sigma }$

Where,

$\sigma =$ Standard deviation

$\mu =$ Mean

$x=$ test score