31. Вычислите: а) \(\frac{11}{30}+\frac{9}{25}:(2−1\frac{23}{35})−1\frac{1}{3}\); б) \(\frac{8}{15}+(2−1\frac{13}{28}):\frac{25}{49}−1\frac{1}{4}\).

1. \(2−1\frac{23}{35}=\frac{12}{35}\). Тогда \(\frac{9}{25}:\frac{12}{35}=\frac{9}{25}\cdot\frac{35}{12}=\frac{21}{20}\). Поэтому \(\frac{11}{30}+\frac{21}{20}−\frac{4}{3}=\frac{11}{30}+\frac{63}{60}−\frac{80}{60}=\frac{1}{12}\).
2. \(2−1\frac{13}{28}=\frac{15}{28}\). Тогда \(\frac{15}{28}:\frac{25}{49}=\frac{15}{28}\cdot\frac{49}{25}=\frac{21}{20}\). Поэтому \(\frac{8}{15}+\frac{21}{20}−\frac{5}{4}=\frac{8}{15}−\frac{1}{5}=\frac{1}{3}\).

Ответ: а) \(\frac{1}{12}\); б) \(\frac{1}{3}\).