10: \(\left(\dfrac{1}{4}-\dfrac{2}{5}\right):\dfrac{3}{8}+\left(\dfrac{3}{4}-\dfrac{8}{5}\right):\dfrac{3}{8}\)
\(=\left(\dfrac{1}{4}-\dfrac{2}{5}+\dfrac{3}{4}-\dfrac{8}{5}\right):\dfrac{3}{8}\)
\(=\left(1-2\right):\dfrac{3}{8}=-1\cdot\dfrac{8}{3}=-\dfrac{8}{3}\)
12: \(\left(\dfrac{4}{15}+\dfrac{3}{5}\right):\dfrac{5}{6}+\left(\dfrac{11}{15}-\dfrac{8}{5}\right):\dfrac{5}{6}\)
\(=\left(\dfrac{4}{15}+\dfrac{3}{5}+\dfrac{11}{15}-\dfrac{8}{5}\right):\dfrac{5}{6}\)
\(=\left(1-1\right):\dfrac{5}{6}=0\)
14: \(\dfrac{11}{15}\cdot\dfrac{-19}{13}+\dfrac{11}{15}\cdot\dfrac{-7}{13}+\dfrac{4}{5}\)
\(=\dfrac{11}{15}\cdot\dfrac{-26}{13}+\dfrac{4}{5}=-\dfrac{22}{15}+\dfrac{12}{15}=-\dfrac{10}{15}=-\dfrac{2}{3}\)
16: \(\dfrac{5}{14}\cdot12\dfrac{1}{2}-\dfrac{5}{14}\cdot5\dfrac{1}{2}\)
\(=\dfrac{5}{14}\left(12+\dfrac{1}{2}-5-\dfrac{1}{2}\right)=\dfrac{5}{14}\cdot7=\dfrac{5}{2}\)
`10)(1/4-2/5):3/8+(3/4-8/5):3/8`
`=(1/4+3/4-2/5-8/5):3/8`
`=(1-2):3/8=(-1):3/8=-8/3`
`12)(4/15+3/5):5/6+(11/15-8/5):5/6`
`=(4/15+11/15+3/5-8/5):5/6`
`=(1-1):5/6=0:5/6=0`
`14)11/15*(-19/13)+11/15*(-7/13)+4/5`
`=11/15.(-19/13-7/13)+4/5`
`=11/15.(-2)+4/5`
`=-22/15+4/5=-10/15=-2/3`
`16)5/14*12 1/2-5/14*5 1/2`
`=5/14*(12 1/2-5 1/2)`
`=5/14*7=5/2`
