Answer
$780$
Work Step by Step
We have a finite series. To find the sum of a finite series, we can use the formula:
$S_n = \frac{n}{2}(a_1 + a_n)$, where $S_n$ is the sum of the series, $n$ is the number of terms in the series, $a_1$ is the first term, and $a_n$ is $nth$ last term.
List the values we are given:
There are 12 terms, so $n = 12$.
$a_1 = 10$
$a_{12} = 120$
Let's plug in the values that we are given into this formula:
$S_{12} = \frac{12}{2}(10 + 120)$
Simplify the fraction:
$S_{12} = 6(10 + 120)$
Evaluate what's in parentheses first:
$S_{12} = 6(130)$
Multiply to solve:
$S_{12} = 780$
