Answer
$504$
Work Step by Step
Sum of the an arithmetic series can be calculated by using formula $S_n=\dfrac{n}{2}(2a_1+(n-1)d)$
Since, from $31$ to $53$ , we have $(\dfrac{53-31}{2})+1=11+1=12$
Here $n=12$
Thus, $S_{12}=\dfrac{12}{2}(2(31)+11(2))=504$
