4.370 Вычислите наиболее удобным способом: a) 9,9 + 40 - 3,9 - 2; 7 6) 20 - 50 - 10,5 + 7; 11 3 11 18 7 B) 5-2-4-3+2; 18 1 r) 3 – 1,6 − 2 + 3,2 + 0,4 + 17.

а) \[9.9 + 4\frac{5}{7} - 3.9 - 2\frac{3}{7} = (9.9 - 3.9) + (4\frac{5}{7} - 2\frac{3}{7}) = 6 + 2\frac{2}{7} = 8\frac{2}{7}\]

б) \[2\frac{1}{6} - 5\frac{5}{11} - 10.5 + 7\frac{1}{3} = 2\frac{1}{6} + 7\frac{1}{3} - 5\frac{5}{11} - 10.5 = 9\frac{1}{2} - 5\frac{5}{11} - 10.5 = 9.5 - 10.5 - 5\frac{5}{11} = -1 - 5\frac{5}{11} = -6\frac{5}{11}\]

в) \[5\frac{11}{18} - \frac{7}{24} - 4\frac{3}{18} - 3\frac{5}{24} + 2\frac{1}{18} = (5\frac{11}{18} - 4\frac{3}{18} + 2\frac{1}{18}) + (-\frac{7}{24} - 3\frac{5}{24}) = (5 - 4 + 2) + (\frac{11}{18} - \frac{3}{18} + \frac{1}{18}) - (\frac{7}{24} + \frac{77}{24}) = 3 + \frac{9}{18} - \frac{84}{24} = 3 + \frac{1}{2} - \frac{7}{2} = 3 - \frac{6}{2} = 3 - 3 = 0\]

г) \[3\frac{4}{5} - 1.6 - 2\frac{1}{3} + 3.2 + 0.4 + 1\frac{7}{15} = 3.8 - 1.6 - 2.333 + 3.2 + 0.4 + 1.466 = (3.8 + 3.2 + 0.4) - (1.6 + 2.333 - 1.466) = 7.4 - 2.467 = 4.933 \approx 4.93\]