1)

[tex] \frac{4}{19} + ( - \frac{5}{19} ) + \frac{7}{19} + ( - \frac{13}{19} ) = \frac{4 - 5 + 7 - 13}{19 } = - \frac{7}{19} [/tex]

2)

[tex]1 \frac{2}{3} + ( - \frac{8}{17} ) + 5 \frac{1}{3} + ( - \frac{9}{17} ) = 7 - \frac{17}{17} = 7 - 1 = 6[/tex]

3)

[tex] - 5 \frac{1}{7} + 4 \frac{4}{7} + 2 \frac{6}{7} + ( - 1 \frac{2}{7} ) = 6 \frac{10}{7} - 6 \frac{3}{7} = \frac{7}{7} = 1[/tex]

4)

[tex]9 \frac{1}{11} + 5 \frac{7}{13} + ( - 8 \frac{3}{11} ) + ( - 5 \frac{7}{13} ) = 9 \frac{1}{11} - 8 \frac{3}{11} =\\= 8 \frac{12}{11} - 8 \frac{3}{11} = \frac{9}{11} [/tex]