Решение:

1. а) $$1\frac{1}{2}+1\frac{1}{3} = \frac{3}{2} + \frac{4}{3} = \frac{9}{6} + \frac{8}{6} = \frac{17}{6} = 2\frac{5}{6}$$
2. б) $$1\frac{1}{4}+2\frac{2}{5} = \frac{5}{4} + \frac{12}{5} = \frac{25}{20} + \frac{48}{20} = \frac{73}{20} = 3\frac{13}{20}$$
3. в) $$2\frac{3}{4}+1\frac{1}{4} = \frac{11}{4} + \frac{5}{4} = \frac{16}{4} = 4$$
4. г) $$3\frac{3}{4}+2\frac{2}{5} = \frac{15}{4} + \frac{12}{5} = \frac{75}{20} + \frac{48}{20} = \frac{123}{20} = 6\frac{3}{20}$$
5. д) $$5\frac{1}{6}-3\frac{1}{3} = \frac{31}{6} - \frac{10}{3} = \frac{31}{6} - \frac{20}{6} = \frac{11}{6} = 1\frac{5}{6}$$
6. е) $$3\frac{7}{4}-1\frac{3}{4} = \frac{19}{4} - \frac{7}{4} = \frac{12}{4} = 3$$
7. ж) $$1\frac{1}{8}+4\frac{5}{9} = \frac{9}{8} + \frac{41}{9} = \frac{81}{72} + \frac{328}{72} = \frac{409}{72} = 5\frac{49}{72}$$
8. з) $$2\frac{3}{5}-1\frac{2}{3} = \frac{13}{5} - \frac{5}{3} = \frac{39}{15} - \frac{25}{15} = \frac{14}{15}$$
9. и) $$5\frac{1}{12}-2\frac{7}{12} = \frac{61}{12} - \frac{31}{12} = \frac{30}{12} = \frac{5}{2} = 2\frac{1}{2}$$
10. к) $$1\frac{2}{5}+1\frac{8}{12} = \frac{7}{5} + \frac{20}{12} = \frac{7}{5} + \frac{5}{3} = \frac{21}{15} + \frac{25}{15} = \frac{46}{15} = 3\frac{1}{15}$$
11. л) $$9\frac{23}{40}-3\frac{3}{28} = \frac{383}{40} - \frac{87}{28} = \frac{2681}{280} - \frac{870}{280} = \frac{1811}{280} = 6\frac{131}{280}$$
12. м) $$5\frac{9}{35}+3\frac{4}{6} = \frac{184}{35} + \frac{22}{6} = \frac{184}{35} + \frac{11}{3} = \frac{552}{105} + \frac{385}{105} = \frac{937}{105} = 8\frac{97}{105}$$