For the following G.P.*, find Sn
0.7, 0.07, 0.007, .....
a = 0.7 = $7/10$, r = $0.07/0.7 = 1/10 < 1$
Sn = $("a"(1 - "r"^"n"))/(1 - "r")$, for r < 1
= $(7/10[1 - (1/10)^"n"])/(1 - 1/10)$
= $7/9 (1 - 1/10^"n")$