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. $$1\frac{8}{9}$$.