№ 1. Вычислить: а) 4,39 + 23,7; 13/20 + 5/8. б) 53,6 − 2,35; 5/9 − 4/12. в) 15,3 · 6,21; 3/10 · 25/27. г) 0,348 : 2,9; 25/7 : 15/14.

а)

1. \(4,39+23,7=4,39+23,70=28,09\).
2. \(\frac{13}{20}+\frac{5}{8}=\frac{26}{40}+\frac{25}{40}=\frac{51}{40}=1\frac{11}{40}\).

б)

1. \(53,6-2,35=53,60-2,35=51,25\).
2. \(\frac{5}{9}-\frac{4}{12}=\frac{5}{9}-\frac{1}{3}=\frac{5}{9}-\frac{3}{9}=\frac{2}{9}\).

в)

1. \(15,3\cdot6,21=95,013\).
2. \(\frac{3}{10}\cdot\frac{25}{27}=\frac{75}{270}=\frac{5}{18}\).

г)

1. \(0,348:2,9=3,48:29=0,12\).
2. \(\frac{25}{7}:\frac{15}{14}=\frac{25}{7}\cdot\frac{14}{15}=\frac{10}{3}=3\frac{1}{3}\).

Ответ: а) 28,09; \(1\frac{11}{40}\). б) 51,25; \(\frac{2}{9}\). в) 95,013; \(\frac{5}{18}\). г) 0,12; \(3\frac{1}{3}\).