11. 2 1/4 : 1 - 3/8 * 7/8 =

11. $$2 \frac{1}{4} : 1 - \frac{3}{8} \cdot \frac{7}{8} = \frac{9}{4} : 1 - \frac{21}{64} = \frac{9}{4} : \frac{64}{64} - \frac{21}{64} = \frac{9}{4} : \frac{64 - 21}{64} = \frac{9}{4} : \frac{43}{64} = \frac{9}{4} \cdot \frac{64}{43} = \frac{9 \cdot 64}{4 \cdot 43} = \frac{9 \cdot 16}{1 \cdot 43} = \frac{144}{43} = 3 \frac{15}{43}$$

Ответ: 3 15/43