#### Answer

$S_{50}=2500$

#### Work Step by Step

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:
$S_{50}=\frac{50}{2}(1+99))=25\times100=2500$