This is a question from A-level 1999 Paper 1. A very simple question that tests you if you know your stuffs. 🙂

The $r^{th}$ term of a series is $3^{r-1} + 2r$. Find the sum of the first $n$ terms.

Ans: $\frac{1}{2} (3^{n}-1)+n(n+1)$