Вычислите: 449. а) 2/3 + 1/4; б) 4/5 - 3/4; в) 1/2 - 1/3; г) 5/6 + 3/8.

Чтобы сложить или вычесть дроби, нужно привести их к общему знаменателю. 449. а) $\frac{2}{3} + \frac{1}{4} = \frac{8}{12} + \frac{3}{12} = \frac{11}{12}$ б) $\frac{4}{5} - \frac{3}{4} = \frac{16}{20} - \frac{15}{20} = \frac{1}{20}$ в) $\frac{1}{2} - \frac{1}{3} = \frac{3}{6} - \frac{2}{6} = \frac{1}{6}$ г) $\frac{5}{6} + \frac{3}{8} = \frac{20}{24} + \frac{9}{24} = \frac{29}{24} = 1\frac{5}{24}$ 450. а) $\frac{1}{2} + \frac{2}{5} = \frac{5}{10} + \frac{4}{10} = \frac{9}{10}$ б) $\frac{1}{2} - \frac{2}{5} = \frac{5}{10} - \frac{4}{10} = \frac{1}{10}$ в) $\frac{1}{4} + \frac{1}{6} = \frac{3}{12} + \frac{2}{12} = \frac{5}{12}$ г) $\frac{9}{10} - \frac{5}{6} = \frac{27}{30} - \frac{25}{30} = \frac{2}{30} = \frac{1}{15}$ 451. а) $\frac{3}{4} + \frac{2}{3} = \frac{9}{12} + \frac{8}{12} = \frac{17}{12} = 1\frac{5}{12}$ б) $\frac{3}{5} - \frac{1}{3} = \frac{9}{15} - \frac{5}{15} = \frac{4}{15}$ в) $\frac{3}{4} - \frac{2}{3} = \frac{9}{12} - \frac{8}{12} = \frac{1}{12}$ г) $\frac{3}{4} + \frac{3}{14} = \frac{21}{28} + \frac{6}{28} = \frac{27}{28}$ 452. а) $\frac{1}{4} - \frac{1}{6} = \frac{3}{12} - \frac{2}{12} = \frac{1}{12}$ б) $\frac{3}{5} + \frac{1}{3} = \frac{9}{15} + \frac{5}{15} = \frac{14}{15}$ в) $\frac{4}{5} + \frac{3}{4} = \frac{16}{20} + \frac{15}{20} = \frac{31}{20} = 1\frac{11}{20}$ г) $\frac{7}{10} - \frac{1}{4} = \frac{14}{20} - \frac{5}{20} = \frac{9}{20}$