Выполни действия с обыкновенными дробями: вычисли примеры на сложение, вычитание и умножение

- 15a) $$\frac{5}{6} - \frac{3}{10} = \frac{5*5}{6*5} - \frac{3*3}{10*3} = \frac{25}{30} - \frac{9}{30} = \frac{16}{30} = \frac{8}{15}$$ - 15б) $2\frac{1}{5} + 3\frac{2}{3} = \frac{2*5+1}{5} + \frac{3*3+2}{3} = \frac{11}{5} + \frac{11}{3} = \frac{11*3}{5*3} + \frac{11*5}{3*5} = \frac{33}{15} + \frac{55}{15} = \frac{88}{15} = 5\frac{13}{15}$$ - 15в) $2 - \frac{1}{3} = \frac{2*3}{3} - \frac{1}{3} = \frac{6}{3} - \frac{1}{3} = \frac{5}{3} = 1\frac{2}{3}$$ - 15г) $4\frac{2}{3} + 5\frac{4}{7} = \frac{4*3+2}{3} + \frac{5*7+4}{7} = \frac{14}{3} + \frac{39}{7} = \frac{14*7}{3*7} + \frac{39*3}{7*3} = \frac{98}{21} + \frac{117}{21} = \frac{215}{21} = 10\frac{5}{21}$$ - 15д) $3\frac{6}{7} - 2\frac{8}{9} = \frac{3*7+6}{7} - \frac{2*9+8}{9} = \frac{27}{7} - \frac{26}{9} = \frac{27*9}{7*9} - \frac{26*7}{9*7} = \frac{243}{63} - \frac{182}{63} = \frac{61}{63}$$ - 16a) $$\frac{3}{10} - \frac{2}{15} = \frac{3*3}{10*3} - \frac{2*2}{15*2} = \frac{9}{30} - \frac{4}{30} = \frac{5}{30} = \frac{1}{6}$$ - 16б) $1\frac{4}{7} + 2\frac{3}{21} = \frac{1*7+4}{7} + \frac{2*21+3}{21} = \frac{11}{7} + \frac{45}{21} = \frac{11*3}{7*3} + \frac{45}{21} = \frac{33}{21} + \frac{45}{21} = \frac{78}{21} = \frac{26}{7} = 3\frac{5}{7}$$ - 16в) $5\frac{1}{4} + 3\frac{8}{11} = \frac{5*4+1}{4} + \frac{3*11+8}{11} = \frac{21}{4} + \frac{41}{11} = \frac{21*11}{4*11} + \frac{41*4}{11*4} = \frac{231}{44} + \frac{164}{44} = \frac{395}{44} = 8\frac{43}{44}$$ - 16г) $4 - 2\frac{2}{3} = \frac{4*3}{3} - \frac{2*3+2}{3} = \frac{12}{3} - \frac{8}{3} = \frac{4}{3} = 1\frac{1}{3}$$ - 16д) $5\frac{1}{4} - 3\frac{7}{8} = \frac{5*4+1}{4} - \frac{3*8+7}{8} = \frac{21}{4} - \frac{31}{8} = \frac{21*2}{4*2} - \frac{31}{8} = \frac{42}{8} - \frac{31}{8} = \frac{11}{8} = 1\frac{3}{8}$$ - 17a) $2 \cdot 6 = 12$$ - 17б) $3 \frac{3}{7} \cdot 4 = \frac{3*7+3}{7} \cdot 4 = \frac{24}{7} \cdot 4 = \frac{24 \cdot 4}{7} = \frac{96}{7} = 13 \frac{5}{7}$$ - 17в) $$\frac{3}{7} \cdot 5 = \frac{3 \cdot 5}{7} = \frac{15}{7} = 2 \frac{1}{7}$$ - 17г) $3 \frac{2}{5} \cdot 4 = \frac{3*5+2}{5} \cdot 4 = \frac{17}{5} \cdot 4 = \frac{17 \cdot 4}{5} = \frac{68}{5} = 13 \frac{3}{5}$$ - 18) **Допущение:** Пример выглядит как $9\frac{2}{7} - 3\frac{8}{15} + 1\frac{7}{9} - 6\frac{2}{7} \cdot 5 \frac{5}{6} - 8 \frac{3}{9} + 6 \frac{2}{4}$. $9\frac{2}{7} - 3\frac{8}{15} + 1\frac{7}{9} - 6\frac{2}{7} \cdot 5 \frac{5}{6} - 8 \frac{3}{9} + 6 \frac{2}{4} = \frac{9*7+2}{7} - \frac{3*15+8}{15} + \frac{1*9+7}{9} - \frac{6*7+2}{7} \cdot \frac{5*6+5}{6} - \frac{8*9+3}{9} + \frac{6*4+2}{4} = \frac{65}{7} - \frac{53}{15} + \frac{16}{9} - \frac{44}{7} \cdot \frac{35}{6} - \frac{75}{9} + \frac{26}{4} = \frac{65}{7} - \frac{53}{15} + \frac{16}{9} - \frac{22}{1} \cdot \frac{5}{3} - \frac{25}{3} + \frac{13}{2} = \frac{65}{7} - \frac{53}{15} + \frac{16}{9} - \frac{110}{3} - \frac{25}{3} + \frac{13}{2} = \frac{65}{7} - \frac{53}{15} + \frac{16}{9} - \frac{135}{3} + \frac{13}{2} = \frac{65}{7} - \frac{53}{15} + \frac{16}{9} - 45 + \frac{13}{2} = -33.15$ **Ответ:** - 15a) $\frac{8}{15}$ - 15б) $5\frac{13}{15}$ - 15в) $1\frac{2}{3}$ - 15г) $10\frac{5}{21}$ - 15д) $\frac{61}{63}$ - 16a) $\frac{1}{6}$ - 16б) $3\frac{5}{7}$ - 16в) $8\frac{43}{44}$ - 16г) $1\frac{1}{3}$ - 16д) $1\frac{3}{8}$ - 17a) $12$ - 17б) $13 \frac{5}{7}$ - 17в) $2 \frac{1}{7}$ - 17г) $13 \frac{3}{5}$ - 18) $-33.15$