a) \(\dfrac{2}{3}+\dfrac{-5}{12}=\dfrac{8}{12}+\dfrac{-5}{12}=\dfrac{3}{12}=\dfrac{1}{4}\)
b) \(\dfrac{3}{5}+\dfrac{-1}{7}=\dfrac{21}{35}+\dfrac{-5}{35}=\dfrac{16}{35}\)
c) \(\left(-3\right)-\dfrac{-2}{9}=\left(-3\right)+\dfrac{2}{9}=-\dfrac{25}{9}\)
d) \(\dfrac{-11}{12}-2=\dfrac{-11}{12}+\dfrac{-2}{1}=\dfrac{-11}{12}+\dfrac{-24}{12}=-\dfrac{35}{12}\)
e) \(\dfrac{3}{8}-\dfrac{1}{5}+\dfrac{3}{40}=\dfrac{15}{40}-\dfrac{8}{40}+\dfrac{3}{40}=\dfrac{15-8+3}{40}=\dfrac{10}{40}=\dfrac{1}{4}\)
f) \(\dfrac{17}{18}-\dfrac{11}{6}-\dfrac{2}{-9}=\dfrac{11}{18}-\dfrac{11}{6}+\dfrac{2}{9}=\dfrac{11}{18}-\dfrac{33}{18}+\dfrac{4}{18}=-\dfrac{18}{18}=-1\)
