Решение:

1)

$$ (20.88 + 18 + 45 + 0.36) \div (19.59 + 11.95) = 84.24 \div 31.54 $$ $$ 84.24 \div 31.54 = 2.67 $$ Ответ: 2.67

2)

$$ \frac{7}{36} \cdot 9 + 8 \cdot \frac{11}{32} + \frac{9}{10} \cdot \frac{5}{18} = \frac{7}{4} + \frac{11}{4} + \frac{1}{4} $$ $$ \frac{7 + 11 + 1}{4} = \frac{19}{4} = 4.75 $$ Ответ: 4.75

3)

$$ (3 \frac{4}{25} + 0.24) \cdot 2.15 + (5.1625 - 2 \frac{3}{16}) \cdot \frac{2}{5} = (3.16 + 0.24) \cdot 2.15 + (5.1625 - 2.1875) \cdot \frac{2}{5} $$ $$ = 3.4 \cdot 2.15 + 2.975 \cdot \frac{2}{5} = 7.31 + 1.19 = 8.50 $$ Ответ: 8.50

4)

$$ 0.364 \div \frac{7}{25} + \frac{5}{16} \cdot \frac{1000}{125} + 2 \frac{1}{2} \cdot 0.8 = 0.364 \cdot \frac{25}{7} + \frac{5}{16} \cdot 8 + 2.5 \cdot 0.8 $$ $$ = 1.3 + 2.5 + 2 = 5.8 $$ Ответ: 5.8