question_answer

In a series of 2n observations, half of them equal a and remaining half equal - a. If the standard deviation of the observations is 2. Than \[\left| a \right|\] is equals

A)  \[\frac{1}{n}\]            

B)  \[\sqrt{2}\]          

C)  \[2\]                

D)  \[\frac{\sqrt{2}}{n}\]