269. Вычислите: 1) $\frac{3}{7} + \frac{4}{9}$ 2) $\frac{8}{9} - \frac{7}{8}$ 3) $\frac{13}{15} - \frac{2}{3}$ 4) $\frac{20}{21} + \frac{3}{7}$ 5) $\frac{17}{18} - \frac{11}{12}$ 6) $\frac{7}{16} + \frac{1}{6}$ 7) $\frac{2}{9} + \frac{5}{6}$ 8) $\frac{10}{21} + \frac{9}{14}$ 9) $\frac{7}{9} - \frac{4}{15}$ 10) $\frac{9}{14} - \frac{3}{7} + \frac{15}{28}$ 11) $\frac{1}{6} + \frac{1}{4} - \frac{1}{8}$ 12) $\frac{13}{18} - \frac{29}{45} + \frac{8}{15}$

Question

Вопрос: $Фото задания: 269. Вычислите: 1) $\frac{3}{7} + \frac{4}{9}$ 2) $\frac{8}{9} - \frac{7}{8}$ 3) $\frac{13}{15} - \frac{2}{3}$ 4)…$ Фото задания

269. Вычислите: 1) $\frac{3}{7} + \frac{4}{9}$ 2) $\frac{8}{9} - \frac{7}{8}$ 3) $\frac{13}{15} - \frac{2}{3}$ 4) $\frac{20}{21} + \frac{3}{7}$ 5) $\frac{17}{18} - \frac{11}{12}$ 6) $\frac{7}{16} + \frac{1}{6}$ 7) $\frac{2}{9} + \frac{5}{6}$ 8) $\frac{10}{21} + \frac{9}{14}$ 9) $\frac{7}{9} - \frac{4}{15}$ 10) $\frac{9}{14} - \frac{3}{7} + \frac{15}{28}$ 11) $\frac{1}{6} + \frac{1}{4} - \frac{1}{8}$ 12) $\frac{13}{18} - \frac{29}{45} + \frac{8}{15}$

Accepted Answer

Решение:

1) $ \frac{3}{7} + \frac{4}{9} = \frac{3 \times 9 + 4 \times 7}{7 \times 9} = \frac{27 + 28}{63} = \frac{55}{63} $
2) $ \frac{8}{9} - \frac{7}{8} = \frac{8 \times 8 - 7 \times 9}{9 \times 8} = \frac{64 - 63}{72} = \frac{1}{72} $
3) $ \frac{13}{15} - \frac{2}{3} = \frac{13 - 2 \times 5}{15} = \frac{13 - 10}{15} = \frac{3}{15} = \frac{1}{5} $
4) $ \frac{20}{21} + \frac{3}{7} = \frac{20 + 3 \times 3}{21} = \frac{20 + 9}{21} = \frac{29}{21} $
5) $ \frac{17}{18} - \frac{11}{12} = \frac{17 \times 2 - 11 \times 3}{36} = \frac{34 - 33}{36} = \frac{1}{36} $
6) $ \frac{7}{16} + \frac{1}{6} = \frac{7 \times 3 + 1 \times 8}{48} = \frac{21 + 8}{48} = \frac{29}{48} $
7) $ \frac{2}{9} + \frac{5}{6} = \frac{2 \times 2 + 5 \times 3}{18} = \frac{4 + 15}{18} = \frac{19}{18} $
8) $ \frac{10}{21} + \frac{9}{14} = \frac{10 \times 2 + 9 \times 3}{42} = \frac{20 + 27}{42} = \frac{47}{42} $
9) $ \frac{7}{9} - \frac{4}{15} = \frac{7 \times 5 - 4 \times 3}{45} = \frac{35 - 12}{45} = \frac{23}{45} $
10) $ \frac{9}{14} - \frac{3}{7} + \frac{15}{28} = \frac{9 \times 2 - 3 \times 4 + 15}{28} = \frac{18 - 12 + 15}{28} = \frac{6 + 15}{28} = \frac{21}{28} = \frac{3}{4} $
11) $ \frac{1}{6} + \frac{1}{4} - \frac{1}{8} = \frac{1 \times 4 + 1 \times 6 - 1 \times 3}{24} = \frac{4 + 6 - 3}{24} = \frac{10 - 3}{24} = \frac{7}{24} $
12) $ \frac{13}{18} - \frac{29}{45} + \frac{8}{15} = \frac{13 \times 5 - 29 \times 2 + 8 \times 6}{90} = \frac{65 - 58 + 48}{90} = \frac{7 + 48}{90} = \frac{55}{90} = \frac{11}{18} $

Ответ:

Решение: