Răspuns:
9.
[tex]x + y = 11.9 \\ \frac{x}{y} = \frac{2}{5} \\ y = \frac{5x}{2} \\ x + \frac{5x}{2} = 11.9 \\ \frac{7x}{2} = 11.9 \\ 7x = 23.8 \\ x = \frac{23.8}{7 } \\ x = 3.4 \\ y = \frac{5 \times 3.4}{2} = \frac{17}{2 } = 8.2[/tex]
10.
[tex]ma = \frac{a + b}{2} = \frac{1 + \frac{1}{2} + \frac{1}{3} + ... + \frac{1}{2015} + 1 + \frac{1}{2} + \frac{2}{3} + \frac{3}{4} + ... + \frac{2014}{2015} }{ 2 } = \frac{2 + 1 + 1 + ... + 1}{2} = \frac{2 + 2014}{2} = \frac{2016}{2} = 1008[/tex]
