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If sum(i=1)^n (xi -a) =n and sum(i=1)^n ...

If `sum_(i=1)^n (x_i -a) =n` and `sum_(i=1)^n (x_i - a)^2 =na` then the standard deviation of variate `x_i`

A

a-1

B

`nsqrt(a-1)`

C

`sqrt(n(a-1))`

D

`sqrt(a-1)`

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