The correct answer is: [tex]\sigma_M[/tex]
Explanation:
σ is a Greek letter, which is called a lowercase sigma. In order to express the standard error of m in an equation, we use σ_M. For example, the formula of the standard error of mean is given as follows:
[tex]\sigma_M = \frac{\sigma}{ \sqrt{N} } [/tex]
Where,
N = sample size
σ = standard deviation
