Let S n = 1 1 3 + 1 + 2 1 3 + 2 3 + 1 + 2 + 3 1 3 + 2 3 + 3 3 + … + 1 + 2 + … , + n 1 3 + 2 3 +…

Let Sn=113+1+213+23+1+2+313+23+33++1+2+,+n13+23+n3 . If 100 Sn=n, then n is equal to:
  1. 200
  2. 199
  3. 99
  4. 19

Solution

Given, Sn=113+1+213+23+1+2+313+23+33++1+2++n13+23++n3

Tn=nn+12nn+122

Tn=2nn+1=21n-1n+1

Sn=2n=1n1n-1n+1

Sn=21-1n+1=2nn+1

Given, 100Sn=n100×2nn+1=n

n+1=200

n=199

Asked in: JEE Main 2017 (09 Apr Online)

Practice more Sequences and Series questions on Aicharya