1.

The value of `sum_(r=0)^(15)r^(2)((""^(15)C_(r))/(""^(15)C_(r-1)))` is equal toA. 1085B. 560C. 680D. 1240

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`.


Discussion

No Comment Found

Related InterviewSolutions