Official solution
S = 1 + 2 \times 3 + 3 \times 5 + 4 \times 7 +....
upto 11th term
General term Tn = n (2n - 1)
\[ \therefore \] Sn = \[\sum {{T_n}} \]
\[ \Rightarrow \] Sn = \[\sum {\left( {2{n^2} - n} \right)} \]
\[ \Rightarrow \] Sn = \[2\sum {{n^2} - \sum r } \]
\[ \Rightarrow \] Sn = \[2\left( {{{n\left( {n + 1} \right)\left( {2n + 1} \right)} \over 6}} \right) - {{n\left( {n + 1} \right)} \over 2}\]
\[ \therefore \] S11 = \[2\left( {{{11\left( {12} \right)\left( {23} \right)} \over 6}} \right) - {{11\left( {12} \right)} \over 2}\]
\[ \Rightarrow \] S11 = 946