\(f,-\dfrac{2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+-\dfrac{2}{5}=\dfrac{-2.4}{12}+\dfrac{3.3}{4.3}-\dfrac{-1}{6}+-\dfrac{2}{5}=\dfrac{1}{12}-\dfrac{-1}{6}+-\dfrac{2}{5}=\dfrac{1-\left(-1\right).2}{12}+-\dfrac{2}{5}=\dfrac{3}{12}-\dfrac{2}{5}=\dfrac{1}{4}-\dfrac{2}{5}=\dfrac{5-2.4}{20}=\dfrac{-3}{20}\)
f, \(\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+\dfrac{-2}{5}=\dfrac{-40}{60}+\dfrac{45}{60}+\dfrac{10}{60}+\dfrac{-24}{60}=\dfrac{-40+45+10+\left(-24\right)}{60}=\dfrac{-9}{60}=\dfrac{-3}{20}\)
\(f=-\dfrac{2}{3}+\dfrac{3}{4}+\dfrac{1}{6}-\dfrac{2}{5}=-\dfrac{40}{60}+\dfrac{45}{60}+\dfrac{10}{60}-\dfrac{24}{60}=\dfrac{-40+45+10-24}{60}\\ =-\dfrac{9}{60}=-\dfrac{3}{20}\)