№1. Вычислите: 1) 2/5 + 3/10; 2) 12/20 − 7/30; 3) 7/8 + 5/6 − 5/24; 4) 15/16 − 15/32 + 51/64.

1) \(\frac{2}{5}+\frac{3}{10}=\frac{4}{10}+\frac{3}{10}=\frac{7}{10}\).

2) \(\frac{12}{20}-\frac{7}{30}=\frac{36}{60}-\frac{14}{60}=\frac{22}{60}=\frac{11}{30}\).

3) \(\frac{7}{8}+\frac{5}{6}-\frac{5}{24}=\frac{21}{24}+\frac{20}{24}-\frac{5}{24}=\frac{36}{24}=1\frac{1}{2}\).

4) \(\frac{15}{16}-\frac{15}{32}+\frac{51}{64}=\frac{60}{64}-\frac{30}{64}+\frac{51}{64}=\frac{81}{64}=1\frac{17}{64}\).

Ответ: 1) \(\frac{7}{10}\); 2) \(\frac{11}{30}\); 3) \(1\frac{1}{2}\); 4) \(1\frac{17}{64}\).