Let xᵢ (1 ≤ i ≤ 10) be ten observations of a random variable x. If Σ(from i=1 to 10)(xᵢ – p) = 3 and Σ(from i=1 to 10)(xᵢ – p)² = 9 where 0 ≠ p ∈ R, then the standard deviation of these observations is:

The variance of 20 observations is 5. If each observation is multiplied by 2 then the new variance of the resulting observations, is:
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If the variance of the terms in an increasing A.P. b?,b?,b?,...,b?? is 90, then the common difference of this A.P. is