已知数列\(\{a_{n}\}\)：\( \dfrac{1}{2}\)，\( \dfrac{1}{3}+ \dfrac{2}{3}\)，\( \dfrac{1}{4}+ \dfrac{2}{4}+ \dfrac{3}{4}\)，\( \dfrac{1}{5}+ \dfrac{2}{5}+ \dfrac{3}{5}+ \dfrac{4}{5}\)，\(…\)，那么数列\(\{b_{n}\}=\left\{ \left. \dfrac{1}{a_{n}a_{n+1}} \right. \right\}\)前\(n\)项的和为\((\)　　\()\)