Задание 3. Вычислите, используя свойства арифметики: 1) 1/2 + 3/4 − 1/4; 2) 5/6 − 1/3 + 1/2; 6) 3/4 · 8/9 − 1/6; 7) 2/3 · 9/10 + 1/4; 11) 7/8 · 4/5 : 1/2 + 3/10; 12) 9/12 − 1/3 · 9/10 : 3/4.

1. \(\frac{1}{2}+\frac{3}{4}-\frac{1}{4}=\frac{1}{2}+\frac{2}{4}=\frac{1}{2}+\frac{1}{2}=1\).
2. \(\frac{5}{6}-\frac{1}{3}+\frac{1}{2}=\frac{5}{6}-\frac{2}{6}+\frac{3}{6}=1\).
3. \(\frac{3}{4}\cdot\frac{8}{9}-\frac{1}{6}=\frac{2}{3}-\frac{1}{6}=\frac{1}{2}\).
4. \(\frac{2}{3}\cdot\frac{9}{10}+\frac{1}{4}=\frac{3}{5}+\frac{1}{4}=\frac{12}{20}+\frac{5}{20}=\frac{17}{20}\).
5. \(\frac{7}{8}\cdot\frac{4}{5}:\frac{1}{2}+\frac{3}{10}=\frac{7}{10}\cdot2+\frac{3}{10}=\frac{17}{10}=1\frac{7}{10}\).
6. \(\frac{9}{12}-\frac{1}{3}\cdot\frac{9}{10}:\frac{3}{4}=\frac{3}{4}-\frac{3}{10}\cdot\frac{4}{3}=\frac{3}{4}-\frac{2}{5}=\frac{15}{20}-\frac{8}{20}=\frac{7}{20}\).

Ответ: 1) 1; 2) 1; 6) 1/2; 7) 17/20; 11) 1 7/10; 12) 7/20.