4) Упростите выражение: 1) \frac{1}{3}a \cdot \frac{7}{12}b; 2) \frac{8}{9}x \cdot 1\frac{4}{5}y; 3) 5m \cdot 2\frac{6}{11}n \cdot 2\frac{5}{14}k.

• 1) $$\frac{1}{3}a \cdot \frac{7}{12}b = \frac{1 \cdot 7}{3 \cdot 12}ab = \frac{7}{36}ab$$
• 2) $$\frac{8}{9}x \cdot 1\frac{4}{5}y = \frac{8}{9}x \cdot \frac{9}{5}y = \frac{8 \cdot 9}{9 \cdot 5}xy = \frac{8}{5}xy = 1\frac{3}{5}xy$$
• 3) $$5m \cdot 2\frac{6}{11}n \cdot 2\frac{5}{14}k = 5m \cdot \frac{28}{11}n \cdot \frac{33}{14}k = \frac{5 \cdot 28 \cdot 33}{11 \cdot 14}mnk = \frac{5 \cdot 2 \cdot 3}{1}mnk = 30mnk$$

Ответ: 1) $$\frac{7}{36}ab$$, 2) $$1\frac{3}{5}xy$$, 3) $$30mnk$$