Let x1,x2,x3,x4 and x5 be the observations with mean m and standard deviation s . The standard deviation of the
observations kx1,kx2,kx3,kx4 and kx5 is
s +k
sk
ks
s
Here, m=Σxi5,s=Σxi25−Σxi52 For observations kx1,kx2,kx3,kx4,kx5,SD=k2Σxi25−kΣxi52 =k2Σxi25−k2Σxi52=kΣxi25−Σxi52=ks