5. $$13 \cdot \frac{5}{17} + 51 \cdot (\frac{1}{17})^2$$ 6. $$11 \cdot \frac{3}{7} - 98 \cdot (\frac{1}{7})^3$$

Решение 5: $$\begin{aligned} 13 \cdot \frac{5}{17} + 51 \cdot (\frac{1}{17})^2 &= \frac{13 \cdot 5}{17} + 51 \cdot \frac{1}{17^2} \\ &= \frac{65}{17} + \frac{51}{289} \\ &= \frac{65 \cdot 17}{17 \cdot 17} + \frac{51}{289} \\ &= \frac{1105}{289} + \frac{51}{289} \\ &= \frac{1105 + 51}{289} \\ &= \frac{1156}{289} \\ &= 4 \end{aligned}$$ Ответ: 4 Решение 6: $$\begin{aligned} 11 \cdot \frac{3}{7} - 98 \cdot (\frac{1}{7})^3 &= \frac{11 \cdot 3}{7} - 98 \cdot \frac{1}{7^3} \\ &= \frac{33}{7} - \frac{98}{343} \\ &= \frac{33}{7} - \frac{2 \cdot 49}{7 \cdot 49} \\ &= \frac{33}{7} - \frac{2}{7} \\ &= \frac{33 - 2}{7} \\ &= \frac{31}{7} \\ &= 4\frac{3}{7} \end{aligned}$$ Ответ: $$4\frac{3}{7}$$