## Precalculus (6th Edition) Blitzer

$1470$ seats
We need to use the formula $a_n =a_1+(n-1) d$ Here, $a_1=25$ and $d=1$ Now, $S_n=\dfrac{n(a_1+a_n)}{2}$ Now, $S_{35}=\dfrac{35(25+59)}{2}=1470$ seats