1. 2. 3.2 ×

$5 \frac{4}{5} + \frac{1}{13} = 5 + \frac{4}{5} +\frac{1}{13} = \\ = 5 + \frac{4 \times 13 + 5}{5 \times 13} = 5 + \frac{52 + 5}{65} = \\ = 5 \frac{57}{65}$
57=3*19
65=5*13

поэтому дробь 57/65 несократима

$1 \frac{2}{5} - \frac{5}{6} = \frac{7}{5} - \frac{5}{6} = \\ = \frac{7 \times 6 - 5 \times 5}{5 \times 6} = \\ = \frac{42 - 25}{30} = \frac{17}{30}$

$2 \times \frac{3}{15} = 2 \times \frac{3}{3 \times 5} = 2 \times \frac{1}{5} = \frac{2}{5}$