std deviation formula

μ= 1/n Σi Xi
σ^2 = 1/n Σ(xi – μ)^2

σ^2 = ΣXi^2/N -　(ΣXi)^2/N^2

3,4,5,6,7
N = 5
ΣXi = 25
ΣXi^2 = 135

μ= 2
σ^2 = 2