Tính tổng

To find the sum of the given series, we can first find the sum of the first and last terms, and then multiply it by the number of terms and divide by 2.

The first term is 1 and the last term is 99.
The number of terms can be found by subtracting the first term from the last term and adding 1: 99 - 1 + 1 = 99.

So, the sum of the series is (1 + 99) * 99 / 2 = 100 * 99 / 2 = 4950.