# What is the sum of the arithmetic sequence 22, 13, 4?

$22 + 13 + 4 = 39$. A very straightforward answer.
However, if one wishes to find it that way (the stupid way), then first notice that this is a simple arithmetic series. Use the formula $S = \frac{n}{2} \left({a}_{1} + {a}_{\setminus \textrm{n}}\right)$ or the formula $S = \frac{n}{2} \left(2 {a}_{1} + \left(n - 1\right) d\right)$ where ${a}_{1}$ is the first term, ${a}_{n}$ is the last term, $d$ is the common difference, $n$ is the number of terms in your series.
Note that both of these are equivalent since ${a}_{n} = {a}_{1} + \left(n - 1\right) d$.
$S = \frac{3}{2} \left(22 + 4\right) = 39$ or $S = \frac{3}{2} \left(2 \setminus \cdot 22 - 9 \setminus \cdot 2\right) = 39.$