Вычислите а) 2/5+1/2, б) 5/6-2/3, в) 8/15+3/10

[latex] \frac{2}{5} + \frac{1}{2} = \frac{2*2}{5*2} + \frac{1*5}{2*5} = \frac{4}{10} + \frac{5}{10} = \frac{4+5}{10} = \frac{9}{10} [/latex] [latex] \frac{5}{6} - \frac{2}{3} = \frac{5}{6} - \frac{2*2}{3*2} = \frac{5}{6} - \frac{4}{6} = \frac{5-4}{6} = \frac{1}{6} [/latex] [latex] \frac{8}{15} + \frac{3}{10} = \frac{8*2}{15*2} + \frac{3*3}{10*3} = \frac{16}{30} + \frac{9}{30} = \frac{16+9}{30} = \frac{25}{30} = \frac{25:5}{30:5} = \frac{5}{6} [/latex]