a,\(\dfrac{2}{5}+\dfrac{3}{4}=\dfrac{8}{20}+\dfrac{15}{20}=\dfrac{23}{20}\)

b,\(\dfrac{2}{3}-\dfrac{3}{8}=\dfrac{16}{24}-\dfrac{9}{24}=\dfrac{7}{24}\)

c,\(\dfrac{3}{7}\times\dfrac{4}{5}=\dfrac{12}{35}\)

d,\(\dfrac{2}{5}\div\dfrac{2}{3}=\dfrac{2}{5}\times\dfrac{3}{2}=\dfrac{6}{10}\)

là tạ đấy