20. 5/3 * 2 1/8 + 5/8 * 1,2.

$$ \frac{5}{3} \cdot 2 \frac{1}{8} + \frac{5}{8} \cdot 1,2 = \frac{5}{3} \cdot \frac{17}{8} + \frac{5}{8} \cdot \frac{12}{10} = \frac{85}{24} + \frac{5}{8} \cdot \frac{6}{5} = \frac{85}{24} + \frac{6}{8} = \frac{85}{24} + \frac{6 \cdot 3}{8 \cdot 3} = \frac{85}{24} + \frac{18}{24} = \frac{103}{24} = 4 \frac{7}{24} $$

Ответ: $$4 \frac{7}{24} $$