Sn = 8[ 1.(1/100) +2.(1/100)^2+...+n(1/100)^n] (1)
(1/100)Sn=8[ 1.(1/100)^2 +2.(1/100)^3+...+n(1/100)^(n+1)] (2)
(1)-(2)
(99/100)Sn = 8{ [1/100+1/100^2+....+1/100^n] - n(1/100)^(n+1) }
=8 { (99/100)[1- (1/100)^n]- n(1/100)^(n+1) }
Sn = (800/99){ (99/100)[1- (1/100)^n]- n(1/100)^(n+1) }
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