Вычислить сумму дробей.

а) $\frac{9}{28} + \frac{3}{7} = \frac{9}{28} + \frac{3 \cdot 4}{7 \cdot 4} = \frac{9}{28} + \frac{12}{28} = \frac{9 + 12}{28} = \frac{21}{28} = \frac{3}{4}$ а) $\frac{9}{13} + \frac{7}{52} = \frac{9 \cdot 4}{13 \cdot 4} + \frac{7}{52} = \frac{36}{52} + \frac{7}{52} = \frac{36 + 7}{52} = \frac{43}{52}$ а) $\frac{4}{15} + \frac{13}{45} = \frac{4 \cdot 3}{15 \cdot 3} + \frac{13}{45} = \frac{12}{45} + \frac{13}{45} = \frac{12 + 13}{45} = \frac{25}{45} = \frac{5}{9}$ а) $\frac{7}{12} + \frac{1}{60} = \frac{7 \cdot 5}{12 \cdot 5} + \frac{1}{60} = \frac{35}{60} + \frac{1}{60} = \frac{35 + 1}{60} = \frac{36}{60} = \frac{3}{5}$ б) $\frac{7}{30} + \frac{11}{300} = \frac{7 \cdot 10}{30 \cdot 10} + \frac{11}{300} = \frac{70}{300} + \frac{11}{300} = \frac{70 + 11}{300} = \frac{81}{300} = \frac{27}{100}$ б) $\frac{5}{42} + \frac{3}{14} = \frac{5}{42} + \frac{3 \cdot 3}{14 \cdot 3} = \frac{5}{42} + \frac{9}{42} = \frac{5 + 9}{42} = \frac{14}{42} = \frac{1}{3}$ б) $\frac{5}{64} + \frac{7}{16} = \frac{5}{64} + \frac{7 \cdot 4}{16 \cdot 4} = \frac{5}{64} + \frac{28}{64} = \frac{5 + 28}{64} = \frac{33}{64}$ б) $\frac{9}{88} + \frac{3}{11} = \frac{9}{88} + \frac{3 \cdot 8}{11 \cdot 8} = \frac{9}{88} + \frac{24}{88} = \frac{9 + 24}{88} = \frac{33}{88} = \frac{3}{8}$ в) $\frac{1}{40} + \frac{3}{5} = \frac{1}{40} + \frac{3 \cdot 8}{5 \cdot 8} = \frac{1}{40} + \frac{24}{40} = \frac{1 + 24}{40} = \frac{25}{40} = \frac{5}{8}$ в) $\frac{5}{17} + \frac{2}{51} = \frac{5 \cdot 3}{17 \cdot 3} + \frac{2}{51} = \frac{15}{51} + \frac{2}{51} = \frac{15 + 2}{51} = \frac{17}{51} = \frac{1}{3}$ в) $\frac{2}{19} + \frac{13}{57} = \frac{2 \cdot 3}{19 \cdot 3} + \frac{13}{57} = \frac{6}{57} + \frac{13}{57} = \frac{6 + 13}{57} = \frac{19}{57} = \frac{1}{3}$ в) $\frac{7}{23} + \frac{3}{46} = \frac{7 \cdot 2}{23 \cdot 2} + \frac{3}{46} = \frac{14}{46} + \frac{3}{46} = \frac{14 + 3}{46} = \frac{17}{46}$ г) $\frac{4}{9} + \frac{5}{36} = \frac{4 \cdot 4}{9 \cdot 4} + \frac{5}{36} = \frac{16}{36} + \frac{5}{36} = \frac{16 + 5}{36} = \frac{21}{36} = \frac{7}{12}$ г) $\frac{17}{36} + \frac{5}{18} = \frac{17}{36} + \frac{5 \cdot 2}{18 \cdot 2} = \frac{17}{36} + \frac{10}{36} = \frac{17 + 10}{36} = \frac{27}{36} = \frac{3}{4}$ г) $\frac{4}{63} + \frac{8}{21} = \frac{4}{63} + \frac{8 \cdot 3}{21 \cdot 3} = \frac{4}{63} + \frac{24}{63} = \frac{4 + 24}{63} = \frac{28}{63} = \frac{4}{9}$ г) $\frac{19}{65} + \frac{4}{13} = \frac{19}{65} + \frac{4 \cdot 5}{13 \cdot 5} = \frac{19}{65} + \frac{20}{65} = \frac{19 + 20}{65} = \frac{39}{65} = \frac{3}{5}$