8 9 11. 12-10- 10 10

11. $$12\frac{8}{10}-10\frac{9}{10} = (12-10) + (\frac{8}{10} - \frac{9}{10}) = 2 - \frac{1}{10} = 1 + 1 - \frac{1}{10} = 1 + \frac{10}{10} - \frac{1}{10} = 1\frac{9}{10}$$.

Ответ: $$1\frac{9}{10}$$