412 Выполните действия: a) 7/9 - 5/12; в) 5/6 + 7/8; д) 13 21/22 - 11 3/55; е) 8 5/40 + 7 10/60.

а) \[\frac{7}{9} - \frac{5}{12} = \frac{7 \cdot 4}{9 \cdot 4} - \frac{5 \cdot 3}{12 \cdot 3} = \frac{28}{36} - \frac{15}{36} = \frac{28-15}{36} = \frac{13}{36}\]

в) \[\frac{5}{6} + \frac{7}{8} = \frac{5 \cdot 4}{6 \cdot 4} + \frac{7 \cdot 3}{8 \cdot 3} = \frac{20}{24} + \frac{21}{24} = \frac{20+21}{24} = \frac{41}{24} = 1\frac{17}{24}\]

д) \[ 13 \frac{21}{22} - 11 \frac{3}{55} = 13 \frac{21 \cdot 5}{22 \cdot 5} - 11 \frac{3 \cdot 2}{55 \cdot 2} = 13 \frac{105}{110} - 11 \frac{6}{110} = (13 - 11) + \frac{105 - 6}{110} = 2 + \frac{99}{110} = 2 + \frac{9}{10} = 2\frac{9}{10} \]

е) \[ 8 \frac{5}{40} + 7 \frac{10}{60} = 8 \frac{1}{8} + 7 \frac{1}{6} = 8 \frac{1 \cdot 3}{8 \cdot 3} + 7 \frac{1 \cdot 4}{6 \cdot 4} = 8 \frac{3}{24} + 7 \frac{4}{24} = (8 + 7) + \frac{3 + 4}{24} = 15 + \frac{7}{24} = 15\frac{7}{24} \]