## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$S_{50}=2500$
The first n term of an arithmetic sequence can be calculated as: $S_n=\frac{n}{2}(a_1+a_n)$ We have to find the sum of the odd numbers from 1 to 99. $a_1=1$ $a_{n}=99$ There are 50 odd numbers from 1 to 99, inclusive. Therefore we can substitute in the formula of the sum, and we get: $S_{50}=\frac{50}{2}(1+99))=25\times100=2500$