The sum of all odd numbers form 1 to 99

The sum of all the odd numbers from 1 to 99 is easy to explain. Take the first and last numbers, 1 and 99. They add up to 100. Then take the next two numbers, 2 and 98. They also add up to 100. If you keep doing this, you will get 25 numbers that can be multiplied by 100. So the answer is 2,500.