21. Выполните сложение и вычитание и выделите целую часть дроби.

Решение:

1. \( \frac{11}{12} + \frac{9}{12} = \frac{11+9}{12} = \frac{20}{12} = 1 \frac{8}{12} = 1 \frac{2}{3} \)

2. \( \frac{7}{13} - \frac{7}{13} = \frac{7-7}{13} = \frac{0}{13} = 0 \)

3. \( \frac{23}{7} - \frac{13}{7} = \frac{23-13}{7} = \frac{10}{7} = 1 \frac{3}{7} \)

4. \( \frac{17}{10} + \frac{7}{10} = \frac{17+7}{10} = \frac{24}{10} = 2 \frac{4}{10} = 2 \frac{2}{5} \)

5. \( \frac{48}{36} - \frac{12}{36} = \frac{48-12}{36} = \frac{36}{36} = 1 \)

6. \( \frac{119}{36} - \frac{11}{36} = \frac{119-11}{36} = \frac{108}{36} = 3 \)

7. \( \frac{677}{66} - \frac{13}{66} = \frac{677-13}{66} = \frac{664}{66} = 10 \frac{4}{66} = 10 \frac{2}{33} \)

8. \( \frac{45}{15} + \frac{7}{15} = \frac{45+7}{15} = \frac{52}{15} = 3 \frac{7}{15} \)

9. \( \frac{50}{7} - \frac{16}{7} = \frac{50-16}{7} = \frac{34}{7} = 4 \frac{6}{7} \)

10. \( \frac{19}{18} + \frac{15}{18} = \frac{19+15}{18} = \frac{34}{18} = 1 \frac{16}{18} = 1 \frac{8}{9} \)

Ответ: 1. 1 \(\frac{2}{3}\); 2. 0; 3. 1 \(\frac{3}{7}\); 4. 2 \(\frac{2}{5}\); 5. 1; 6. 3; 7. 10 \(\frac{2}{33}\); 8. 3 \(\frac{7}{15}\); 9. 4 \(\frac{6}{7}\); 10. 1 \(\frac{8}{9}\).