Question

Let S_n denote the sum of first n terms of an A.P. If S_2n = 3 S_n then S_3n/S_n is –

• A. 4
• B. 6
• C. 8
• D. None

Answer 1

Answer: (B)

6

Answer 2

Put n = 1 ® S₂ = 3S₁

\ T₁ = S₁

& T₂ = S₂ – S₁ = 2S₁ = 2T₁

\ AP is : T₁, 2T₁, 3T₁, 4T₁….

\ $\frac { S _ { 3 n } } { S _ { n } }$= = $\frac { 6 \mathrm {~T} _ { 1 } } { \mathrm {~T} _ { 1 } }$ = 6