[tex]\left(\dfrac{2}{5}x+\dfrac{5}{8}\right)+\left(\dfrac{1}{5}x-\dfrac{1}{4}\right)=\left(\dfrac{2}{5}x+\dfrac{1}{5}x\right)+\left(\dfrac{5}{8}-\dfrac{1}{4}\right)\\\\=\dfrac{2+1}{5}x+\left(\dfrac{5}{8}-\dfrac{1\cdot2}{4\cdot2}\right)=\dfrac{3}{5}x+\left(\dfrac{5}{8}-\dfrac{2}{8}\right)\\\\=\dfrac{3}{5}x+\dfrac{5-2}{8}=\boxed{\dfrac{3}{5}x+\dfrac{3}{8}}[/tex]
