11. 12 -10

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

Ответ: $$1 \frac{9}{10}$$