## Intermediate Algebra for College Students (7th Edition)

$1430$
Sum of the an arithmetic series can be calculated by using formula $S_n=\dfrac{n}{2}(2a_1+(n-1)d)$ Our aim is to determine a formula for the general term of the arithmetic sequence $a_n$. Such as: $a_n=a_1+(n-1)d$ For $n=26$ $s_{26}=13(a_1+a_{26})$ ...(1) Now, $a_n=a_1+(n-1)d$ $\implies a_{26}=a_1+(25)(2)=80$ From equation (1), we have $s_{26}=13(30+80)=1430$