Computational Formula
n             SX2 Ð (SX)2
ns2 =                    n
n                    N
n
n X X2
n
 1 1    N = 4
n 0 0    X = 2
n 6 36
n 1 1
n  SX =  8       SX2 = 38     
n SS =  38 Ð 82/4    = 38 Ð 16 = 22