Question

The sum of the series $1+2\times 3+3\times 5+4\times 7+.....$

• A. $915$
• B. $946$
• C. $945$
• D. $916$

Answer 1

Answer: (B)

$946$

$T_r=r(2r-1)$

$S=\sum 2r^2-\sum r$

$S=\frac{2.n(n+1)(2n+1)}{6}-\frac{n(n+1)}{2}$

$S_{11}=\frac{2}{6}\left(11\right)\left(12\right)\left(12\right)-\frac{11\left(12\right)}{2}=\left(44\right)\left(23\right)-66=946$