#### Answer

true

#### Work Step by Step

RECALL:
The sum of the first $n$ terms of an arithmetic sequence can be found using the formula:
$S_n=\dfrac{n}{2}\left(a + a_n\right)$
where
$n$ = number of terms
$a$ = first term
$a_n$ = $n^{th}$ term
The formula above can be rewritten as:
$S_n = n\left(\dfrac{a+a_n}{2}\right)$
Notice that in the formula above, $\dfrac{a+a_n}{2}$ represents the average of $a$ and $a_n$.
Thus, the given statement is true.