a)\(\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+\dfrac{-2}{5}=\dfrac{-40+45-\left(-10\right)+\left(-24\right)}{60}\)\(=\dfrac{-9}{60}=\dfrac{-3}{20}\)
b)\(\dfrac{-2}{3}+\dfrac{-1}{5}+\dfrac{3}{4}-\dfrac{5}{6}-\dfrac{-7}{10}=\dfrac{-40-12+45-50+42}{60}\)
\(=\dfrac{-15}{60}=\dfrac{-1}{4}\)
T.I.C.K mk nhé!!^_^