If the Random Sample $X _ { 1 } , \ldots \ldots , X _ { n }$

Essay

If the random sample $X _ { 1 } , \ldots \ldots , X _ { n }$ is taken from a normal distribution with mean value $\mu$ and standard deviation $\sigma$ , then regardless of the sample size n, the sample mean $\bar { X }$ is distributed with expected value __________ and standard deviation __________.