## Precalculus (6th Edition)

$3240$
We are looking for the sum of the first 80 positive integers. Use the formula $S_n=\frac{n}{2}(a_1+a_n)$ with $n=80, a_1=1, a_{80}=80$: $S_n=\frac{n}{2}(a_1+a_n)$ $S_{80}=\frac{80}{2}(1+80)$ $S_{80}=40*81$ $S_{80}=\boxed{3240}$