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The value of `sum_(r=0)^(15)r^(2)((""^(15)C_(r))/(""^(15)C_(r-1)))` is equal toA. 1085B. 560C. 680D. 1240 |
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Answer» Correct Answer - c We have, ` ((""^(15)C_(r))/(""^(15)C_(r-1)))= (n-r +1)/(r)` `therefore sum_(r=1)^(15) r^(2) ((""^(15)C_(r))/(""^(15)C_(r-1)))sum_(r=1)^(15) r^(2)((15 - r +1)/(r)) = sum_(r=1)^(15) r (16 -r)` `= 16 sum_(r=1)^(15) r- sum_(r=1)^(15) r^(2)` `= (16xx15xx15)/(2) - (15xx16xx31)/(6) = 680`. |
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