1,5 21. 1

$$\frac{1,5}{1 + \frac{1}{5}} = \frac{1,5}{\frac{5+1}{5}} = \frac{1,5}{\frac{6}{5}} = \frac{1,5 \cdot 5}{6} = \frac{7,5}{6} = 1,25$$

Ответ: 1,25