Thursday, 1 December 2016

sequences and series - Where i'm doing wrong in the solution?

I'm learning Progression and Series with myself.At current about Arithmetic Progression.I'm stuck in a problem from sometime.I don't know why my answer is coming different from book.


Problem-




The sum of n terms of two A.P's are in the ratio of 7n+1:4n+27 , find the ratio of their 11th term.




My solution-
To find the ratio of 11th term i used formula of finding Tn= Sn-Sn-1 .First I calculated ratio of sum of 11th term and 10th term and calculated the difference.

Image




Answer in the book :- 4/3

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