51. Найдите разность: 1) 7 5/6 - 3 2/3; 2) 8 5/12 - 6 7/20; 3) 11 1/12 - 5 7/9.

1.

\( 7 \frac{5}{6} - 3 \frac{2}{3} = (7-3) + (\frac{5}{6} - \frac{2}{3}) = 4 + (\frac{5}{6} - \frac{2 \cdot 2}{3 \cdot 2}) = 4 + (\frac{5}{6} - \frac{4}{6}) = 4 + \frac{1}{6} = 4 \frac{1}{6} \)

2.

\( 8 \frac{5}{12} - 6 \frac{7}{20} = (8-6) + (\frac{5}{12} - \frac{7}{20}) = 2 + \frac{5 \cdot 5 - 7 \cdot 3}{60} = 2 + \frac{25 - 21}{60} = 2 + \frac{4}{60} = 2 + \frac{1}{15} = 2 \frac{1}{15} \)

3.

\( 11 \frac{1}{12} - 5 \frac{7}{9} = (11-5) + (\frac{1}{12} - \frac{7}{9}) = 6 + \frac{1 \cdot 3 - 7 \cdot 4}{36} = 6 + \frac{3 - 28}{36} = 6 - \frac{25}{36} \)

Заменим 6 на \( 5 + \frac{36}{36} \)

\( 5 + \frac{36}{36} - \frac{25}{36} = 5 + \frac{36-25}{36} = 5 + \frac{11}{36} = 5 \frac{11}{36} \)