Let the original 8 data be x 1, x2, …, x8, with an average value of X- and a variance of S2;

The data newly added to the group is x9, the average value is X-', and the variance is s'2, then

x-= 18(x 1+x2+…+x8),∴x 1+x2+…+x8=8x-=40，

S2 = 18(x 2 1+x22+…+x28)-x-2，

∴x2 1+x22+…+x28=8(s2+x-2)=2 16，

∴x-2= 19(x 1+x2+…+x8+x9)= 19(40+4)=449，

s′2 = 19(x 2 1+x22+…+x28+x29)-x-′2

= 19(2 16+ 16)-4492= 1528 1.