Câu $1$
$a)\dfrac{-2}{3}+\dfrac{3}{4}+\dfrac{-5}{6}$
$=\dfrac{-8}{12}+\dfrac{9}{12}+\dfrac{-10}{12}$
$=\dfrac{-9}{12}$
$=-\dfrac{3}{4}$
$b)\dfrac{15}{7}.\dfrac{8}{5}-\dfrac{15}{7}.\dfrac{3}{5}$
$=\dfrac{15}{7}(\dfrac{8}{5}-\dfrac{3}{5})$
$=\dfrac{15}{7}.\dfrac{5}{5}$
$=\dfrac{15}{7}.1$
$=\dfrac{15}{7}$
$c)(2-\dfrac{7}{10}):(\dfrac{5}{7}+\dfrac{3}{14})$
$=(\dfrac{20}{10}-\dfrac{7}{10}):(\dfrac{10}{14}+\dfrac{3}{14})$
$=\dfrac{13}{10}:\dfrac{13}{14}$
$=\dfrac{13}{10}.\dfrac{14}{13}$
$=\dfrac{7}{5}$
Câu $2$
$a)\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{3}{2}$
$\Leftrightarrow\dfrac{2}{3}x=\dfrac{3}{2}+\dfrac{1}{2}$
$\Leftrightarrow\dfrac{2}{3}x=2$
$\Leftrightarrow x=2:\dfrac{2}{3}$
$\Leftrightarrow x=3$
Vậy $x=3$
$b)3\dfrac{1}{4}:x=0,5$
$\Leftrightarrow\dfrac{13}{4}:x=\dfrac{1}{2}$
$\Leftrightarrow x=\dfrac{13}{4}:\dfrac{1}{2}$
$\Leftrightarrow x=\dfrac{13}{2}$
Vậy $x=\dfrac{13}{2}$
$c)3\dfrac{1}{3}x+5\dfrac{3}{4}=-0,25$
$\Leftrightarrow\dfrac{10}{3}x+\dfrac{23}{4}=-\dfrac{1}{4}$
$\Leftrightarrow\dfrac{10}{3}x=-\dfrac{1}{4}-\dfrac{23}{4}$
$\Leftrightarrow\dfrac{10}{3}x=-6$
$\Leftrightarrow x=-6:\dfrac{10}{3}$
$\Leftrightarrow x=-\dfrac{9}{5}$
Vậy $x=-\dfrac{9}{5}$
