3) 4/7 * 1/12 6) 7 * 2/21 2. Вычисли: ...

3) $\frac{4}{7} \cdot \frac{1}{12} = \frac{4}{84} = \frac{1}{21}$. 6) $7 \cdot \frac{2}{21} = \frac{14}{21} = \frac{2}{3}$. 2. Вычисли: Числитель: $3 \frac{1}{8} : \frac{15}{16} - \frac{1}{4} = \frac{25}{8} \cdot \frac{16}{15} - \frac{1}{4} = \frac{10}{3} - \frac{1}{4} = \frac{40-3}{12} = \frac{37}{12} = 3 \frac{1}{12}$. Знаменатель: $(\frac{2}{7} + \frac{5}{21}) : 1 \frac{4}{7} = (\frac{6+5}{21}) : \frac{11}{7} = \frac{11}{21} \cdot \frac{7}{11} = \frac{1}{3}$. Дробь: $\frac{37}{12} : \frac{1}{3} = \frac{37}{12} \cdot 3 = \frac{37}{4} = 9 \frac{1}{4}$. Вторая часть: $(8 \frac{7}{12} - 2 \frac{5}{8}) : 2 \frac{1}{6} = (8 \frac{14}{24} - 2 \frac{15}{24}) : \frac{13}{6} = (7 \frac{38}{24} - 2 \frac{15}{24}) : \frac{13}{6} = 5 \frac{23}{24} : \frac{13}{6} = \frac{143}{24} \cdot \frac{6}{13} = \frac{11}{4} = 2 \frac{3}{4}$. Знаменатель: $1 \frac{7}{12} : (\frac{3}{8} + \frac{5}{12}) = \frac{19}{12} : (\frac{9+10}{24}) = \frac{19}{12} : \frac{19}{24} = \frac{19}{12} \cdot \frac{24}{19} = 2$. Дробь: $2 \frac{3}{4} : 2 = \frac{11}{4} \cdot \frac{1}{2} = \frac{11}{8} = 1 \frac{3}{8}$. Итого: $9 \frac{1}{4} - 1 \frac{3}{8} - 1 \frac{9}{20} = 9 \frac{10}{40} - 1 \frac{15}{40} - 1 \frac{18}{40} = 8 \frac{50}{40} - 1 \frac{15}{40} - 1 \frac{18}{40} = 6 \frac{17}{40}$. 4. Реши уравнение: а) $2 \frac{1}{3}x + 1 \frac{1}{15}x = 6 \frac{4}{5} \implies (2 \frac{5}{15} + 1 \frac{1}{15})x = 6 \frac{12}{15} \implies 3 \frac{6}{15}x = 6 \frac{12}{15} \implies \frac{51}{15}x = \frac{102}{15} \implies x = \frac{102}{15} \cdot \frac{15}{51} = 2$. б) $(x - \frac{3}{5}x) \cdot 1 \frac{1}{24} - 1 \frac{3}{4} = 1 \frac{1}{6} \implies \frac{2}{5}x \cdot \frac{25}{24} = 1 \frac{1}{6} + 1 \frac{3}{4} \implies \frac{5}{12}x = \frac{7}{6} + \frac{7}{4} \implies \frac{5}{12}x = \frac{14+21}{12} \implies \frac{5}{12}x = \frac{35}{12} \implies x = 7$.