What is the sum of the first 13 terms of an arithmetic progression if the first term is -10 and last term is 26?

Solution (By Examveda Team)

$$\eqalign{ & {S_n} = \frac{n}{2}\left[ {a + l} \right] \cr & {S_{13}} = \frac{{13}}{2}\left[ { - 10 + 26} \right] \cr & {S_{13}} = \frac{{13}}{2}\left[ {16} \right] \cr & {S_{13}} = 104 \cr} $$