JEE Math Practice Question

A function f(x) is given by $$f(x) = {{{5^x}} \over {{5^x} + 5}}$$, then the sum of the series $$f\left( {{1 \over {20}}} \right) + f\left( {{2 \over {20}}} \right) + f\left( {{3 \over {20}}} \right) + ....... + f\left( {{{39} \over {20}}} \right)$$ is equal to :

1. A.$${{{39} \over 2}}$$
2. B.$${{{19} \over 2}}$$
3. C.$${{{49} \over 2}}$$
4. D.$${{{29} \over 2}}$$