1.

If `s_n=sum_(r < s) (1/(nC_r)+1/(nC_s)) and t_n=sum_(r < s)(r/(nC_r)+s/(nC_s)),` then `t_n/s_n=`A. n-1B. n+1C. `(n)/(2)`D. none of these

Answer» Correct Answer - c
We have,
`t_(n) =sum_(rlts) ( (r)/(""^(n)C_(r))+(s)/(""^(n)C_(s)))`
`rArr t_(n) =sum_(rgts)( (r)/(""^(n)C_(r))+(s)/(""^(n)C_(s)))`
`rArr t_(n) =sum_(n-rltn-s)( (n-r)/(""^(n)C_(n-r))+(n-s)/(""^(n)C_(n-s)))`
`rArr t_(n) =sum_(rlts)( (1)/(""^(n)C_(r))+(1)/(""^(n)C_(s)))- sum_(rlt s)( (r)/(""^(n)C_(r))+(s)/(""^(n)C_(s)))`
`rArr t_(n) = n s_(n) - t_(n) rArr (t_(n))/(s_(n)) = (n)/(2)`


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