Statistics h/w question?

for 20 items of data sigma x= 22 and sigma x^2= 55
find the mean and rmsd of the data.

mean = 22/20 = 1.1
rmsd = √( 55/20 - 1.1²) = 1.241

∑x = 22

∑x^2 = 55

n=20

Mean = ∑x/n =22/20 = 1.1

RMSD = √(∑x^2/n)

= √55/20

= 1.6583123951777

= 1.66