a) \( \frac{2}{3} a \cdot \frac{5}{12} b = \frac{2 \cdot 5}{3 \cdot 12} ab = \frac{10}{36} ab = \frac{5}{18} ab \)
б) \( \frac{8}{9} \cdot \frac{15}{4} = \frac{8 \cdot 15}{9 \cdot 4} = \frac{120}{36} = \frac{10}{3} = 3\frac{1}{3} \)
в) \( 5m \cdot 2 \cdot \frac{7}{12} k = 10mk \cdot \frac{7}{12} = \frac{70}{12} mk = \frac{35}{6} mk = 5\frac{5}{6} mk \)
г) \( \frac{2}{5} \cdot 2 \cdot \frac{1}{4} y = \frac{2 \cdot 2 \cdot 1}{5 \cdot 4} y = \frac{4}{20} y = \frac{1}{5} y \)
д) \( 1 \cdot \frac{5}{12} y = \frac{5}{12} y \)
Ответ: а) 5/18 ab
б) 10/3
в) 35/6 mk
г) 1/5 y
д) 5/12 y