\( \dfrac{1}{2.3}+\dfrac{2}{3.5}+\dfrac{3}{5.8}\\=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{2}(\dfrac{2}{3}-\dfrac{2}{5})+\dfrac{1}{3}.(\dfrac{3}{5}-\dfrac{3}{8})\\=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{2}.\dfrac{2}{3}-\dfrac{1}{2}.\dfrac{2}{5}+\dfrac{1}{3}.\dfrac{3}{5}-\dfrac{1}{3}.\dfrac{3}{8}\\=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}\\=\dfrac{1}{2}-\dfrac{1}{8}\\=\dfrac{4-1}{8}=\dfrac{3}{8}\)