1. Вычислите: а) 1/6 + 5/12; б) 2/3 − 3/5; в) 3/5 · 4/9; г) 7/9 : 21/25.

а) \(\frac{1}{6}+\frac{5}{12}=\frac{2}{12}+\frac{5}{12}=\frac{7}{12}\).

б) \(\frac{2}{3}-\frac{3}{5}=\frac{10}{15}-\frac{9}{15}=\frac{1}{15}\).

в) \(\frac{3}{5}\cdot\frac{4}{9}=\frac{12}{45}=\frac{4}{15}\).

г) \(\frac{7}{9}:\frac{21}{25}=\frac{7}{9}\cdot\frac{25}{21}=\frac{25}{27}\).

Ответ: а) \(\frac{7}{12}\); б) \(\frac{1}{15}\); в) \(\frac{4}{15}\); г) \(\frac{25}{27}\).