Explicație pas cu pas:
27.a)
[tex]\frac{1}{120} + \frac{2}{120} + ... + \frac{119}{120} = \frac{ \frac{119 \cdot 120}{2} }{120} = \frac{119}{2} \\ [/tex]
b)
[tex]\frac{2}{50} + \frac{4}{50} + \frac{6}{50} +... + \frac{48}{50} = \\ = \frac{2}{50} \cdot (1 + 2 + 3 + ... + 24) \\ = \frac{1}{25} \cdot \frac{24 \cdot 25}{2} = \frac{24}{2} = 12[/tex]
