Let Sn denote the sum of first n terms of an A.P.. If S2n = 3Sn, then the ratio S3n / 5n is equal to
(a) 4 (b) 6
(c) 8 (d) 10

• Que. should be if S2n=3Sn, then the ratio S3n/Sn=?
  ans. (b)
• 10 years agoHelpfull: Yes(8) No(3)
• ans is 6.
  S2n=3sn
  2n(2n+1)/2=3n(n+1)/2
  ,
  n=1
  after s3n/sn=6
• 10 years agoHelpfull: Yes(6) No(0)
• we know the formula
  Sn=n(n+1)/2
  given,
  S2n = 3Sn
  now,
  put the formula in above equation
  2n(2n+1)/2= 3n(n+1)/2
  2(2n+1) = 3(n+1)
  4n+2 = 3n+3
  n=1
  now we find
  S3n / 5n
  now again put formula of Sn
  3n(3n+1)/2/5n
  put value of n=1
  3(4)/2*5 = 12/10=1.2
  ans is 1.2 which is not given in option
  
• 10 years agoHelpfull: Yes(1) No(6)