Question

1) If a G.P. S2n-Sn = ?
Note: 2n and n is the below power
2) If n=10,mean =12 and sigma x²=1530 then variance is ?

Pls reply quickly!!!!!!!!!!!

Answer 1

S2n=ar(2n-1)
Sn=ar(n-1)
___________
ar(n)