1) 4/5 + 2/5 2) 2/9 + 4/7 3) 13/10 - 5/10 4) 11/12 - 1/12

Решение:

1. \( \frac{4}{5} + \frac{2}{5} = \frac{6}{5} = 1 \frac{1}{5} \)
2. \( \frac{2}{9} + \frac{4}{7} = \frac{2 \cdot 7}{9 \cdot 7} + \frac{4 \cdot 9}{7 \cdot 9} = \frac{14}{63} + \frac{36}{63} = \frac{50}{63} \)
3. \( \frac{13}{10} - \frac{5}{10} = \frac{8}{10} = \frac{4}{5} \)
4. \( \frac{11}{12} - \frac{1}{12} = \frac{10}{12} = \frac{5}{6} \)

Ответ: 1) \( 1 \frac{1}{5} \); 2) \( \frac{50}{63} \); 3) \( \frac{4}{5} \); 4) \( \frac{5}{6} \).