$3-\dfrac{2}{3}+\dfrac{4}{15}=\dfrac{1}{3}+\dfrac{4}{15}=\dfrac{5}{15}+\dfrac{4}{15}=\dfrac{9}{15}$
$\dfrac{19}{5}×\dfrac{1}{2}-\dfrac{3}{20}=\dfrac{19}{10}-\dfrac{3}{20}=\dfrac{38}{20}-\dfrac{3}{20}=\dfrac{35}{20}=\dfrac{7}{4}$
$\dfrac{5}{2}:\dfrac{3}{4}+\dfrac{4}{7}×\dfrac{2}{5}=\dfrac{5}{2}×\dfrac{4}{3}+\dfrac{8}{35}=\dfrac{20}{6}+\dfrac{8}{35}=\dfrac{700}{210}+\dfrac{48}{210}=\dfrac{748}{210}=\dfrac{374}{105}$
$\dfrac{1}{7} + (2-\dfrac{7}{4}) = \dfrac{1}{7} + \dfrac{1}{4} = \dfrac{4}{28} + \dfrac{7}{28} = \dfrac{11}{28}$
