19:
a: =1,35:2,7+2+(2/5:3/2)*(21/5-43/40)
\(=\dfrac{1}{2}+2+\dfrac{2}{5}\cdot\dfrac{2}{3}\cdot\left(\dfrac{21}{5}-\dfrac{43}{40}\right)\)
\(=\dfrac{5}{2}+\dfrac{4}{15}\cdot\dfrac{25}{8}=\dfrac{10}{3}\)
b: \(=\left[\left(6+\dfrac{3}{5}-3-\dfrac{3}{14}\right)\cdot\dfrac{35}{6}\right]:\dfrac{79}{10}\)
\(=\left(3+\dfrac{3}{5}-\dfrac{3}{14}\right)\cdot\dfrac{35}{6}\cdot\dfrac{10}{79}\)
\(=\dfrac{237}{70}\cdot\dfrac{350}{6\cdot79}=\dfrac{5}{2}\)
c: \(=\dfrac{\dfrac{1}{8}-\dfrac{1}{5}+\dfrac{1}{7}}{3\left(\dfrac{1}{8}-\dfrac{1}{5}+\dfrac{1}{7}\right)}+\dfrac{\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{5}}{\dfrac{3}{2}\left(\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{5}\right)}\)
=1/3+1:3/2
=1/3+2/3
=1
