Найдите сумму: 1) 12 3/8 + 8 1/6; 3) 9 8/21 + 4 11/14...

**50. Найдите сумму:** 1) $12 \frac{3}{8} + 8 \frac{1}{6} = 12 \frac{9}{24} + 8 \frac{4}{24} = 20 \frac{13}{24}$ 2) $3 \frac{13}{15} + 6 \frac{7}{10} = 3 \frac{26}{30} + 6 \frac{21}{30} = 9 \frac{47}{30} = 10 \frac{17}{30}$ 3) $9 \frac{8}{21} + 4 \frac{11}{14} = 9 \frac{16}{42} + 4 \frac{33}{42} = 13 \frac{49}{42} = 14 \frac{7}{42} = 14 \frac{1}{6}$ 4) $8 \frac{5}{9} + 7 \frac{3}{4} + 12 \frac{7}{12} = 8 \frac{20}{36} + 7 \frac{27}{36} + 12 \frac{21}{36} = 27 \frac{68}{36} = 28 \frac{32}{36} = 28 \frac{8}{9}$ **51. Найдите разность:** 1) $7 \frac{5}{6} - 3 \frac{2}{3} = 7 \frac{5}{6} - 3 \frac{4}{6} = 4 \frac{1}{6}$ 2) $8 \frac{5}{12} - 6 \frac{7}{20} = 8 \frac{25}{60} - 6 \frac{21}{60} = 2 \frac{4}{60} = 2 \frac{1}{15}$ 3) $11 \frac{11}{12} - 5 \frac{7}{9} = 11 \frac{33}{36} - 5 \frac{28}{36} = 6 \frac{5}{36}$ 4) $9 \frac{17}{24} - 8 \frac{11}{36} = 9 \frac{51}{72} - 8 \frac{22}{72} = 1 \frac{29}{72}$ **52. Выполните вычитание:** 1) $3 \frac{1}{16} - ?rac{1}{8} = 3 \frac{1}{16} - ?rac{2}{16} = 2 \frac{17}{16} - ?rac{2}{16} = 2 \frac{15}{16}$ 2) $7 \frac{9}{20} - 5 \frac{17}{30} = 7 \frac{27}{60} - 5 \frac{34}{60} = 6 \frac{87}{60} - 5 \frac{34}{60} = 1 \frac{53}{60}$ 3) $4 \frac{2}{7} - 1 \frac{4}{9} = 4 \frac{18}{63} - 1 \frac{28}{63} = 3 \frac{81}{63} - 1 \frac{28}{63} = 2 \frac{53}{63}$ 4) $8 \frac{5}{36} - 1 \frac{43}{108} = 8 \frac{15}{108} - 1 \frac{43}{108} = 7 \frac{123}{108} - 1 \frac{43}{108} = 6 \frac{80}{108} = 6 \frac{20}{27}$ 5) $9 \frac{7}{9} - 4 \frac{5}{6} = 9 \frac{14}{18} - 4 \frac{15}{18} = 8 \frac{32}{18} - 4 \frac{15}{18} = 4 \frac{17}{18}$ 6) $6 \frac{7}{32} - 2 \frac{11}{48} = 6 \frac{21}{96} - 2 \frac{22}{96} = 5 \frac{117}{96} - 2 \frac{22}{96} = 3 \frac{95}{96}$ **53. Решите уравнение:** 1) $10 \frac{5}{8} - x = 7 \frac{3}{5}$ $x = 10 \frac{5}{8} - 7 \frac{3}{5} = 10 \frac{25}{40} - 7 \frac{24}{40} = 3 \frac{1}{40}$ Ответ: $3 \frac{1}{40}$ 2) $(x - 2 \frac{7}{8}) + 3 \frac{5}{6} = 4 \frac{2}{3}$ $x - 2 \frac{7}{8} = 4 \frac{2}{3} - 3 \frac{5}{6} = 4 \frac{4}{6} - 3 \frac{5}{6} = 3 \frac{10}{6} - 3 \frac{5}{6} = ?rac{5}{6}$ $x = ?rac{5}{6} + 2 \frac{7}{8} = ?rac{20}{24} + 2 \frac{21}{24} = 2 \frac{41}{24} = 3 \frac{17}{24}$ Ответ: $3 \frac{17}{24}$ **54. Решение:** 1) Скорость по течению: $20 \frac{1}{2} + 1 \frac{7}{8} = 20 \frac{4}{8} + 1 \frac{7}{8} = 21 \frac{11}{8} = 22 \frac{3}{8}$ км/ч. 2) Скорость против течения: $20 \frac{1}{2} - 1 \frac{7}{8} = 20 \frac{4}{8} - 1 \frac{7}{8} = 19 \frac{12}{8} - 1 \frac{7}{8} = 18 \frac{5}{8}$ км/ч. Ответ: $22 \frac{3}{8}$ км/ч; $18 \frac{5}{8}$ км/ч. **55. Вычислите удобным способом:** 1) $(\frac{1}{4} + \frac{3}{4}) + (\frac{2}{5} + \frac{3}{5}) = 1 + 1 = 2$ 2) $(\frac{4}{5} + \frac{1}{5}) + (\frac{1}{3} + \frac{2}{3}) = 1 + 1 = 2$ 3) $(2 \frac{4}{7} + 3 \frac{3}{7}) + (1 \frac{2}{9} + 4 \frac{7}{9}) + \frac{11}{14} = 6 + 6 + \frac{11}{14} = 12 \frac{11}{14}$ **56. Преобразуйте и вычислите:** 1) $0,2 + \frac{1}{7} = \frac{1}{5} + \frac{1}{7} = \frac{7}{35} + \frac{5}{35} = \frac{12}{35}$ 2) $\frac{7}{16} - 0,12 = 0,4375 - 0,12 = 0,3175$ 3) $4,85 - 2 \frac{13}{24} = 4 \frac{17}{20} - 2 \frac{13}{24} = 4 \frac{102}{120} - 2 \frac{65}{120} = 2 \frac{37}{120}$ 4) $7 \frac{8}{21} - 4,375 = 7 \frac{8}{21} - 4 \frac{3}{8} = 7 \frac{64}{168} - 4 \frac{63}{168} = 3 \frac{1}{168}$