а) $$\frac{3}{5} + \frac{2}{5} = \frac{5}{5} = 1$$
б) $$\frac{8}{10} - \frac{3}{10} = \frac{5}{10} = \frac{1}{2}$$
в) $$\frac{31}{100} + \frac{31}{100} = \frac{62}{100} = \frac{31}{50}$$
Ответ: а) $$1$$, б) $$\frac{1}{2}$$, в) $$\frac{31}{50}$$