635. Выполните действия: а) 3/4 : 5/6 + 2 1/2 · 2/5 − 1 : 1 1/6; б) 2 3/4 : (1 1/2 − 2/5) + (3/4 + 5/6) : 3 1/6; в) (2/15 + 7/12) · 30/43 − 2 : 2 1/2 · 5/32.

а)

\(\frac{3}{4}:\frac{5}{6}+2\frac{1}{2}\cdot\frac{2}{5}-1:1\frac{1}{6}\)

\(=\frac{3}{4}\cdot\frac{6}{5}+\frac{5}{2}\cdot\frac{2}{5}-1\cdot\frac{6}{7}\)

\(=\frac{9}{10}+1-\frac{6}{7}=\frac{19}{10}-\frac{6}{7}=\frac{133-60}{70}=\frac{73}{70}=1\frac{3}{70}.\)

б)

\(2\frac{3}{4}:(1\frac{1}{2}-\frac{2}{5})+(\frac{3}{4}+\frac{5}{6}):3\frac{1}{6}\)

\(=\frac{11}{4}:\left(\frac{3}{2}-\frac{2}{5}\right)+\left(\frac{9}{12}+\frac{10}{12}\right):\frac{19}{6}\)

\(=\frac{11}{4}:\frac{11}{10}+\frac{19}{12}:\frac{19}{6}\)

\(=\frac{11}{4}\cdot\frac{10}{11}+\frac{19}{12}\cdot\frac{6}{19}=\frac{5}{2}+\frac{1}{2}=3.\)

в)

\(\left(\frac{2}{15}+\frac{7}{12}\right)\cdot\frac{30}{43}-2:2\frac{1}{2}\cdot\frac{5}{32}\)

\(=\left(\frac{8}{60}+\frac{35}{60}\right)\cdot\frac{30}{43}-\frac{2}{5/2}\cdot\frac{5}{32}\)

\(=\frac{43}{60}\cdot\frac{30}{43}-\frac{4}{5}\cdot\frac{5}{32}=\frac{1}{2}-\frac{1}{8}=\frac{3}{8}.\)

Ответ: а) \(1\frac{3}{70}\); б) \(3\); в) \(\frac{3}{8}\).