\(a,\dfrac{3}{4}+\dfrac{2}{5}+\dfrac{1}{4}+\dfrac{3}{5}=\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=\dfrac{4}{4}+\dfrac{5}{5}=1+1=2\)
\(b,\dfrac{2}{3}+\dfrac{3}{4}\times\dfrac{4}{5}\times\dfrac{5}{6}=\dfrac{2}{3}+\dfrac{3}{6}=\dfrac{2}{3}+\dfrac{1}{2}=\dfrac{4}{6}+\dfrac{3}{6}=\dfrac{7}{6}\\ c,\dfrac{4}{3}-\dfrac{2}{3}+\dfrac{1}{5}-\dfrac{1}{3}=\left(\dfrac{4}{3}-\dfrac{2}{3}-\dfrac{1}{3}\right)+\dfrac{1}{5}=\dfrac{1}{3}+\dfrac{1}{5}=\dfrac{5}{15}+\dfrac{3}{15}=\dfrac{8}{15}\)
\(d,\dfrac{4}{5}\times\dfrac{3}{7}+\dfrac{4}{5}\times\dfrac{4}{7}=\dfrac{4}{5}\times\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{4}{5}\times\dfrac{7}{7}=\dfrac{4}{5}\times1=\dfrac{4}{5}\\ e,\dfrac{2}{5}\times\dfrac{7}{4}-\dfrac{2}{5}\times\dfrac{3}{7}=\dfrac{2}{5}\times\left(\dfrac{7}{4}-\dfrac{3}{7}\right)=\dfrac{2}{5}\times\dfrac{37}{28}=\dfrac{37}{70}\)
=(3/4+1/4)+(2/5+3/5)
= 1 + 1 =2
\(\dfrac{3}{4}\)+\(\dfrac{2}{5}+\dfrac{1}{4}\)+\(\dfrac{3}{5}\)
=\(\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)
=\(1+1\)
=2
