What is sum of all positive odd numbers from 1 to 100?

The answer is 2500.

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$\sum_0^{49}({1+2n}) = \sum_0^{49}(1)+ \sum_0^{49}(2n) = 50 + \frac{2\times49\times50}{2} = 2500$

I have used the fact that $\sum_1^n{k} = \frac{n(n+1)}{2}$