[tex] - 4.2 + 3.8 = - 0.4[/tex]

[tex]2.7 + ( - 6.3) = 2.7 - 6.3 = - 3.6[/tex]

[tex] - \frac{2}{7} + ( - \frac{5}{8} ) = - \frac{2}{7} - \frac{5}{8} = \\ - \frac{16}{56 } - \frac{35}{56} = - \frac{51}{56} [/tex]

[tex]8 \frac{5}{6} + ( - 9 \frac{7}{12} ) = 8 \frac{10}{12 } - 9 \frac{7}{12} = \\ 8 \frac{10}{12} - 8 \frac{19}{12} = - \frac{9}{12} = - \frac{3}{4} = - 0.75[/tex]

1) -4,2 + 3,8 = -0,4

2) 2,7 + (-6,3) = 2,7 - 6,3 = -3,6

3) (-2/7) + (-5/8) = - ((2×8+5×7)/56) = - 51/56

4) 8 5/6 + (-9 7/12) = 106/12 - 115/12 = -9/12 = -3/4 = -0,75