Задание 42. Вычислите. А. 1) \(\frac{2}{5}\) от 10; 2) \(\frac{2}{9}\) от 18; 3) \(\frac{3}{7}\) от 35; 4) \(\frac{3}{5}\) от 25; 5) \(\frac{5}{8}\) от 16; 6) \(\frac{1}{2}\) от \(\frac{6}{7}\); 7) \(\frac{1}{3}\) от \(\frac{21}{25}\); 8) \(\frac{2}{3}\) от \(\frac{12}{17}\); 9) \(\frac{3}{8}\) от \(\frac{5}{9}\); 10) \(\frac{7}{10}\) от \(\frac{30}{31}\); 11) \(\frac{3}{5}\) от \(\frac{10}{21}\); 12) \(\frac{2}{7}\) от \(\frac{35}{36}\); 13) \(\frac{11}{15}\) от \(\frac{25}{44}\); 14) \(\frac{12}{35}\) от \(\frac{77}{80}\); 15) \(\frac{9}{11}\) от \(\frac{55}{63}\).

Чтобы найти дробь от числа, умножаем число на эту дробь.

1. \(10\cdot\frac{2}{5}=\frac{20}{5}=4\).
2. \(18\cdot\frac{2}{9}=\frac{36}{9}=4\).
3. \(35\cdot\frac{3}{7}=\frac{105}{7}=15\).
4. \(25\cdot\frac{3}{5}=\frac{75}{5}=15\).
5. \(16\cdot\frac{5}{8}=\frac{80}{8}=10\).
6. \(\frac{6}{7}\cdot\frac{1}{2}=\frac{6}{14}=\frac{3}{7}\).
7. \(\frac{21}{25}\cdot\frac{1}{3}=\frac{21}{75}=\frac{7}{25}\).
8. \(\frac{12}{17}\cdot\frac{2}{3}=\frac{24}{51}=\frac{8}{17}\).
9. \(\frac{5}{9}\cdot\frac{3}{8}=\frac{15}{72}=\frac{5}{24}\).
10. \(\frac{30}{31}\cdot\frac{7}{10}=\frac{210}{310}=\frac{21}{31}\).
11. \(\frac{10}{21}\cdot\frac{3}{5}=\frac{30}{105}=\frac{2}{7}\).
12. \(\frac{35}{36}\cdot\frac{2}{7}=\frac{70}{252}=\frac{5}{18}\).
13. \(\frac{25}{44}\cdot\frac{11}{15}=\frac{275}{660}=\frac{5}{12}\).
14. \(\frac{77}{80}\cdot\frac{12}{35}=\frac{924}{2800}=\frac{33}{100}\).
15. \(\frac{55}{63}\cdot\frac{9}{11}=\frac{495}{693}=\frac{5}{7}\).

Ответ: 1) 4; 2) 4; 3) 15; 4) 15; 5) 10; 6) \(\frac{3}{7}\); 7) \(\frac{7}{25}\); 8) \(\frac{8}{17}\); 9) \(\frac{5}{24}\); 10) \(\frac{21}{31}\); 11) \(\frac{2}{7}\); 12) \(\frac{5}{18}\); 13) \(\frac{5}{12}\); 14) \(\frac{33}{100}\); 15) \(\frac{5}{7}\).