₉ ₉
If Σ (xᵢ - 5) = 9 and If Σ (xᵢ - 5)² = 45 then the standard deviation of the 9 items x₁, x₂,..., x₉ is
ᶦ⁼¹ ᶦ⁼¹

a. 3
b. 9
c. 4
d. 2