Latest Elitmus Aptitude Question SOLUTION: the infinite sum 1+(4/7)+(9/7^2)+(16/7^3)+.........? options A>27/14 B>29/13 C>49/27 D>256/147

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(#M40038228) ELITMUS Category question Keep an EYE

the infinite sum 1+(4/7)+(9/7^2)+(16/7^3)+.........?
options
A>27/14
B>29/13
C>49/27
D>256/147

Asked In Elitmus ashish (9 years ago)

Unsolved Read Solution (3)

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Read Solution (3) :

Kataria Deepak  (9 years ago)

S = 1 + 4/7 + 9/7^2 + 16/7^3 + 25/7^4 +...
Dividing both the side by 7
S/7 = 1/7 + 4/7^2 + 9/7^3 +...
Subtracting eqn.
6S/7 = 1 + 3/7 + 5/7^2 + 7/7^3 + ....
6S/7^2 = 1/7 + 3/7^2 + 5/7^3
Subtracting again
36S/49 = 1 + 2/7 + 2/7^2 + 2/7^3
take 2/7 outside.....then it will be a onfinite GP.....1 + 1/7 + 1/7^2.....ETC.........ie 7/6.......and u will get 49/27

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raushan kumar  (9 years ago)

@ pranoj plz tm sequence series prh lo...

ans is 49/27. tn = n^2/7^n-1.

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Pranoy Bej  (9 years ago)

ANSWER--> C
Because
1+4/7+9/49+16/343+25/2401+..... = 1.76+...
now the 6th term = 36/16807= 0.002
so going through the option we find that 49/27=1.814 which is closest value
hence it it the right choice

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