1 11/2-2 3/5=

$$1 \frac{11}{2} - 2 \frac{3}{5} = \frac{13}{2} - \frac{13}{5} = \frac{13\cdot 5}{2\cdot 5} - \frac{13 \cdot 2}{5 \cdot 2} = \frac{65}{10} - \frac{26}{10} = \frac{39}{10} = 3 \frac{9}{10} = 3,9$$

Ответ: 3,9