a: \(\dfrac{-3}{5}+\dfrac{7}{21}+\dfrac{-4}{5}+\dfrac{7}{5}\)
\(=\left(-\dfrac{3}{5}-\dfrac{4}{5}+\dfrac{7}{5}\right)+\dfrac{7}{21}\)
\(=0+\dfrac{1}{3}=\dfrac{1}{3}\)
b: \(\left(\dfrac{1}{4}+\dfrac{-5}{13}\right)-\left(\dfrac{8}{13}-\dfrac{2}{11}\right)-\dfrac{3}{-4}\)
\(=\dfrac{1}{4}+\dfrac{-5}{13}-\dfrac{8}{13}+\dfrac{2}{11}+\dfrac{3}{4}\)
\(=\left(\dfrac{1}{4}+\dfrac{3}{4}\right)+\left(-\dfrac{5}{13}-\dfrac{8}{13}\right)+\dfrac{2}{11}\)
\(=1-1+\dfrac{2}{11}=\dfrac{2}{11}\)
c: \(\dfrac{11}{15}\cdot\dfrac{4}{7}+1\dfrac{3}{7}\cdot\dfrac{11}{15}-\dfrac{11}{15}\)
\(=\dfrac{11}{15}\left(\dfrac{4}{7}+\dfrac{10}{7}-1\right)\)
\(=\dfrac{11}{15}\cdot1=\dfrac{11}{15}\)
