[tex] \frac{2}{50} + \frac{4}{50} + \frac{6}{50} + ... + \frac{48}{50} = \\ \\ = \frac{2 + 4 + 6 + ... + 48}{50} = \\ \\ = \frac{2(1 + 2 + 3 + ... + 24)}{50} = \\ \\ = \frac{1 + 2 + 3 + ... + 24}{25} = \\ \\ = \frac{ \frac{24 \times (24 + 1)}{2} }{25} = \frac{12 \times 25}{25} = 12[/tex]
