172. Найдите сумму: 1)-2 +(-4); 2)-0,37+(-0,94); 3)-4,72+(-0,8); 4) -3\frac{6}{11}+(-5\frac{7}{11}); 5) \frac{7}{9}+(-\frac{11}{15}); 6) -3\frac{11}{12}+(-4\frac{9}{16}).

1) -2 + (-4) = -2 - 4 = -6

2) -0,37 + (-0,94) = -0,37 - 0,94 = -1,31

3) -4,72 + (-0,8) = -4,72 - 0,8 = -5,52

4) $$-3\frac{6}{11}+(-5\frac{7}{11}) = -3\frac{6}{11} - 5\frac{7}{11} = -(3+5) - (\frac{6}{11} + \frac{7}{11}) = -8 - \frac{13}{11} = -8 - 1\frac{2}{11} = -9\frac{2}{11}$$

5) $$\frac{7}{9}+(-\frac{11}{15}) = \frac{7}{9} - \frac{11}{15} = \frac{7 \cdot 5}{9 \cdot 5} - \frac{11 \cdot 3}{15 \cdot 3} = \frac{35}{45} - \frac{33}{45} = \frac{2}{45}$$

6) $$-3\frac{11}{12}+(-4\frac{9}{16}) = -3\frac{11}{12} - 4\frac{9}{16} = -3\frac{11 \cdot 4}{12 \cdot 4} - 4\frac{9 \cdot 3}{16 \cdot 3} = -3\frac{44}{48} - 4\frac{27}{48} = -(3+4) - (\frac{44}{48} + \frac{27}{48}) = -7 - \frac{71}{48} = -7 - 1\frac{23}{48} = -8\frac{23}{48}$$

Ответ: 1) -6; 2) -1,31; 3) -5,52; 4) $$-9\frac{2}{11}$$; 5) $$\frac{2}{45}$$; 6) $$-8\frac{23}{48}$$.