\(=\dfrac{1}{3}\left(\dfrac{3}{2\times5}+\dfrac{3}{5\times8}+...+\dfrac{3}{215\times218}\right)\\ =\dfrac{1}{3}\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+...+\dfrac{1}{215}-\dfrac{1}{218}\right)\\ =\dfrac{1}{3}\left(\dfrac{1}{2}-\dfrac{1}{218}\right)=\dfrac{1}{3}\times\dfrac{54}{109}=\dfrac{18}{109}\)
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