Question

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

(A) 4 

(B) 6 

(C) 8

(D) 10

Answer 1

Answer is (B)

Let first term be a and common difference be d.

Then, S_2n = 3S_n